The Spaniard, whose team needed a stoppage-time penalty by Grant Leadbitter to edge it, said: “It was a game we had under control.
“We could have won, three, four, five-nil. It was a game we could have won easily but in the last 10 minutes we conceded one goal.
“The important thing is we managed to win the game and it is the sort of game we have to win this season.”
Leadbitter also scored Boro’s first-half opener, a sizzling long-range free-kick, and now has six goals for the campaign.
And Karanka hailed the former Ipswich Town and Sunderland player’s composure.
“His first was a brilliant goal and the penalty came at a difficult time for any player to stand up and score,” he said.
“Grant is a great example to the other players.
“He is one of those who impressed me when I first came here (last November).
“He is the kind of player who is a strong character and is always working. In bad moments he is always there.”
While Boro go to Cardiff next, Town host Wigan Athletic, who suffered a sixth successive away defeat, 3-1 at Blackburn Rovers.
Manager Uwe Rosler, whose side led through James Perch, said: “I don’t think we deserved that. I’m sitting here not being really unhappy in general about our performance.”
Liam Coogans, recently signed from Airdrie, scored his first Town goal as the Under 18s won 3-1 at Colchester United.
Sam Wardle and Rekeil Pyke got the other goals.
Harry Clibbens, the son of Town chief executive Nigel, skippered the Under 16s to a 3-1 win at Leeds.
Brighouse Town suffered a last-gasp 2-1 defeat by Ashton United in their FA Cup first round qualifying tie.
AFC Emley were 1-0 winners at Lincoln Moorlands Railway in the Northern Counties East League First Division.