Town, who led the table going into October after their 1-0 win at Ipswich Town, are now fourth after taking four points from the last 18.
Next up is a home game against Wigan Athletic in front of the Sky Sports cameras on Monday, November 28.
Former Town manager Warnock’s Cardiff won 3-2 in South Wales – his third victory in six games at the helm – and have hauled themselves out of the drop zone after being second-bottom when he arrived.
The 67-year-old, who led Town to promotion to the Championship in 1995, believes his side can climb the table further, and that Wagner’s can challenge for a place in the Premier League.
“The side Huddersfield have now is the best they have had for many, many years,” he said.
“We were a different type of side when I was there. Now they pass it 15 times to our four!
“Having said that, we had a decent side at Huddersfield and I think the fans will remember we had some exciting times.
“Moving into the new stadium and Jeppo (Ronnie Jepson), who is here at Cardiff with me, and Andy Booth did ever so well for us.
“It’s a great club and although I did enjoy beating them, I wish them every success.”
But Warnock believes the second automatic promotion place and the play-off places are wide open.
“Other than Newcastle, and to be honest, we should have got a draw up there, I think Huddersfield can beat anyone on their day,” he said. "It’s that kind of league this season.
“You’ve got to try and go on a bit of a run and Huddersfield have had one or two difficult results of late.
“David (Wagner) tried to change things against us, but we still managed to score from set-pieces.
“But overall it looks good for them and I think it is credit to (chairman) Dean Hoyle.
“I think he has done a fantastic job. What he has done for the club is great.
“I honestly felt it was a brave decision to bring David in as manager but it has proven to be a fabulous decision.
“I bet Dean can’t believe the way they are playing football.”
Right-back Tommy Smith and midfielder Philip Billing both got their first goals of the season at the Cardiff City Stadium, where Town have lost on all five of their visits.