Brentford had showed early glimpses of their attacking game which saw the Terriers destroyed 3-0 at Griffin Park but Lou Macari's men soon regained their compsure.
Early Bees pressure saw Steve Hunt shoot across the face of goal in the first minute.
Hunt's effort was followed in the 4th minute when Paul Evans forced Martyn Margetson into a desperate save after spilling the ball from his rasping shot.
The Terriers lacked a threat down the left wing and John Thorrington had been targetted as a threat by Brentford and was duly well watched.
Town were determined not to subside, however, and they weathered the storm both on and off the pitch (even the wind was against them at a rainswept McAlpine) to gradually take control of the game.
The midfield battle was won by Thomas Heary and Kenny Irons who closed down most of the efforts to get balls whipped into Ben Burgess and Lloyd Owusu, both of whom were well marshalled by the excellent partnership of Jerel Ifil and Kevin Gray in the continuing absence of Nathan Clarke, who failed a late fitness test.
Up front, Andy Booth and Delroy Facey probably felt a little isolated, with Paul Smith and his defenders kept increasingly busy by Town, but Booth still managed to drop a lob onto Smith's bar after 17 minutes as a forewarning of things to come.
Towards the end of the first half, Town were back in control and could have been 1-0 up through Andy Booth but his goal was quickly ruled out for handball after 33 minutes.
Booth had cause for complaint after being ruled offside 10 minutes into the second half when he tucked away his second 'goal' from a cross by Kenny Irons - a decision which drew howls of derision from the McAlpine crowd.
Irons had had a good match in midfield. He provided plenty of telling passes, tracked back, and had a second half shot saved by Paul Smith.
With two 'goals' disallowed, Town had no room to be complacent and there was a sharp reminder with 7 minutes to go when Brentford captured the ball in midfield and swiftly counter-attacked.
Steve Sidwell played a one-two with LLoyd Owusu and then forced Martyn Margetson into a superb one-handed save to keep Town in the tie.
Sidwell's effort would have been an injustice as Town fully deserved to take a lead to Griffin Park for the second leg but couldn't find a goal - Booth's hard work late on saw him hit the side netting with both sides tiring.
Read Mel Booth's match report in the Examiner on Monday. Have your say on the match and the decider at Griffin Park in the messageboard below. Comments with full name and location will be considered for publication in the Examiner.
Town (4-4-2): Margetson, Moses, Gray, Ifil, G. Evans, Thorrington, Irons, Heary (Hay 79), Holland, Booth, Facey
Subs not used: P. Evans, Beech, Mattis, Delaney
Brentford (4-4-2): Smith, Anderson, Ingimarsson, Powell, P. Evans, Owusu, Rowlands, Dobson, Hunt, Burgess, Sidwell
Subs not used: Gottskalksson, Boxall, Williams, O'Connor, Theobald
Referee: Graham Laws (Whitley Bay)
Attendance: 16,523 (1,632 Away Fans)
92 mins: Ifil cleared with Sidwell and Owusu lurking.
91 mins: Margetson saved from Owusu.
91 mins: 3 minutes of added time were indicated as the tension rose markedly.
91 mins: Burgess' right footed shot was blocked by Gareth Evans and cleared by Ifil.
90 mins: Thorrington ran into a wall of defenders and Brentford countered again.
89 mins: Irons crossed for Hay but his header flew wide of goal despite the efforts of Facey.
88 mins: Rowlands' cross/shot was on target and Margetson made the save and provented the corner.
87 mins: Moses coolly helped the ball away to safety after Gareth Evans allowed Owusu to get away.
86 mins: Moses headed away the Brentford set piece as the crowd screamed offside.
85 mins: Chances were opening as both sides tired. Irons' corner to the far post was won by Booth but cleared by Brentford. Booth's next header from the next corner hit the side netting! Half of the stadium though he had scored!
84 mins: Sidwell forced a superb one-handed save from Margetson as Brentford countered quickly from poor play by Irons.
83 mins: Holland won another corner off Ijah Anderson. Irons' early corner was wasted - straight at Smith.
82 mins: Holland lofted the ball into the area and Paul Smith allowed it to bounce before punching it out with Hay lurking for a simple nod.
81 mins: A poor Moses header was cleared by Ifil and Thorrington took up the baton to attack.
80 mins: Town re-shaped with Holland in the middle and Hay on the left.
79 mins: Chris Hay was stripped down and ready to come on as the referee booked Thorrington for his persistent fouling. Heary was replaced by Hay.
78 mins: Both sides were getting tired and the McAlpine was still wet as the rain started up again. No mistakes were possible.
77 mins: Paul Smith clutched the ball as it drifted towards the far corner.
76 mins: A poor delivery from Paul Evans summed up his afternoon - Irons and Heary had done their job in midfield so far.
75 mins: Irons got back for a defensive header as Brentford flew downfield on the counter-attack with Gareth Evans selling himself too early and Owusu charging down to the Town area.
74 mins: Facey was off balance and looked tired as he picked the wrong option and crossed poorly.
73 mins: Gray recovered to deny Owusu after the big striker appeared to have got the better of him.
72 mins: Burgess' flicked header was inches wide from a corner.
71 mins: Irons had a shot go straight down the 'keeper's throat - an easy save as Town piled the pressure on.
70 mins: Hunt's cross was good for Burgess but his touch was heavy.
68 mins: Andy Booth missed his kick in the penalty area as the ball flew in enticingly.
67 mins: Margetson's first touch was heavy and needed to put it out of play quickly as Owusu bore down on him. Rowlands' shot from the throw-in was wide.
66 mins: Holland'cross was headed away by Sidwell
65 mins: Owusu conceded another corner after Andy Booth tried to get on the end of Thorrington's set piece.
64 mins: Irons' whipped in free kick was punched away for a corner by Paul Smith.
63 mins: Sidwell conceded a free kick and the vociferous Town support demanded and got a booking for the Bees player.
62 mins: Lou Macari decided to warm up the subs as Evans' corner was poor.
60 mins: Moses put Thorrington through but the American was robbed by Hunt. Dobson blatantly shoved Holland off the ball and the linesman stopped play.
58 mins: Margetson collected the corner as Bees players waited patiently.
57 mins: Booth cleared from Anderson's cross. Hunt's shot looped off a Town defender from a corner.
56 mins: Irons' early ball found Andy Booth in the air and he netted again! The linesman drew woeful shouts from the crowd as he flagged for offside!
55 mins: Facey's shot was palmed into the side netting after a long ball from Margetson was flicked on by Booth with Dobson ball watching.
54 mins: Booth's turn and shot was parried.
53 mins: The game was getting physical as Brentford tried to impose themselves on the game.
51 mins:Rowlands' cross almost found Owusu but the effort was cleared.
50 mins: Irons won the ball off Hunt but Holland wasted posession and Town aggressively closed down the Brentford midfield immediately.
49 mins: Burgess was penalised pulling Ifil down.
47 mins: Evans tackled Owusu and won a throw-in.
The Terriers weathered an early storm from the Bees and ended the first half on top as they applied themselves to the task ahead after some early scares at the McAlpine.
Steve Hunt shot across the face of goal in the first minute and Paul Evans' effort was spilled away by Margetson before Town improved.
Andy Booth had several close headers following a 17th minute chance which fell onto the Brentford crossbar and away. Town were comfortable without looking too dangerous during the first half.
45 mins: Only 1 minute of added time was indicated as Town continued to improve. Irons was penalised for a late challenge on Rowlands.
43 mins: Holland turned Dobson and crossed for Andy Booth who beat Darren Powell to a stooping header but missed the target.
42 mins: Burgess tried a falling curler which drifted just wide - their first genuine chance for a long time.
41 mins: There had been a quiet passage of play, with little goalmouth action, as the struggle in midfield absorbed the fans.
33 mins: The ball was in the back of the net courtesy of Andy Booth but the goal didn't count because of a clear infringement (handball) by the talismanic Town striker.
32 mins: Margetson helped his defenders clear the decks.
30 mins: Anderson caught Thorrington narrowly offside as the American shaped up to dash for the ball with a diagonal run.
29 mins: The rain cleared as Town continued to press. They won a free kick which Kenny Irons delivered to the far post - Andy Booth's header came off a defender and was cleared.
27 mins: Booth laid the ball off for Chris Holland who fired a shot in but Facey was ruled offside.
25 mins: Holland's shot was parried away by the 'keeper on the half volley after interference from Booth.
23 mins: Town were becoming more comfortable. Irons delivered another back post set piece which Andy Booth coundn't direct under close attention by Powell.
21 mins: Thorrington fell to the ground after almost getting past Hunt and was penalised for kicking out!
20 mins: Holland's attempt was gathered by Smith.
19 mins: Gareth Evans' shot was blocked but Town tried again and eventually won another free kick after switching play and attacking Anderson.
17 mins: Powell was penalised for backing into Facey. The set piece by Irons found Andy Booth who got a nick on it but fell against the crossbar!!!
16 mins: Anderson fired in a shot after a burst of pressure by Brentford.
15 mins: Margetson came off his line to confidently claim the ball.
14 mins: Rowlands intercepted a Town ball and selected another attack. Town were finding it hard to close down the more effective Bees side.
13 mins: Facey chased down a long ball and was shoulder-charged away by Darren Powell who challenged for the ball.
11 mins: Margetson cleared Moses' back pass as Brentford piled the pressure on once more.
8 mins: Ingimarsson flicked a Bees set piece just wide - Brentford were ever dangerous with dead balls.
7 mins: Thorrington picked up the ball and tried to beat Anderson but trickled out for a goal kick as Brentford immediately targetted him for double marking.
6 mins: Owusu was beaten in the air by Moses who put the ball out for another corner after Holland was caught in possession.
5 mins: Owusu was trying to annoy Margetson at a corner.
4 mins: Thorrington was harshly penalised for a trip on Anderson. Anderson slid the ball to Paul Evans who fired in a shot on goal which was spilled by Margetson for a corner.
3 mins: Ifil was fouled by Owusu and Town won a free kick to relieve the pressure.
1 min: Steve Hunt shot across goal after Town went asleep at a throw-in - Heary allowed Hunt in for a shooting chance on Margetson's goal in the rain.
1 min: Brentford launched their first long ball and immediately went on the offensive.
15:00 - Kick-off
14:55 - The McAlpine crowd cheered loudly as the Town team came out onto the pitch to greet their supporters.
14:50 - Rain was lashing down in Huddersfield.
The clouds were closing in as 3pm approached.
Lou Macari fielded Jerel Ifil in central defence to replace Nathan Clarke, who had not recovered from injury. He also went for a cautious midfield, including Thomas Heary at the expense of Chris Hay who dropped to the bench alongside Chris Beech and Damien Delaney.
The McAlpine was enjoying sunny but cool weather, interrupted by the occasional shower early on.