Wigan made it five league games unbeaten under manager Uwe Rosler as they beat Derby to knock the Rams out of the top two.
The Latics had the better of the first half with Nick Powell, Emmerson Boyce and James McArthur missing the target.
The only goal came when Jean Beausejour played a one-two with Callum McManaman before firing the ball over Lee Grant from the edge of the box.
Simon Dawkins and Chris Martin squandered chances to equalise.
Wigan are up to 11th in the table and only three points off the play-offs, six points closer than they were when Rosler took over on the back of five straight defeats last month.
Derby's run comes to an end
Derby had been unbeaten in their last nine matches, winning eight and drawing the other. They moved into second place in the Championship on Sunday by winning 2-1 at Barnsley
Derby came into the game in second place and unbeaten in nine matches but were second best for large periods of the game.
Powell fired tamely wide for Wigan from 15 yards and Boyce headed off-target before McArthur sent a dipping shot over the bar.
Beausejour put a cross into the side-netting and Roger Espinoza volleyed wide late in the first half.
After the break, the visitors finally took a deserved lead when Beausejour and McManaman, who had only been on the pitch for seconds, exchanged passes following a short corner and the Chilean finished from 18 yards.
Derby belatedly started creating chances and Dawkins should have done better when he took a touch from Conor Sammon's ball and saw his shot deflected wide. Will Hughes had a shot parried by Ali Al Habsi, who denied Sammon the rebound.
And with five minutes left they should have equalised when Martin reached Andre Wisdom's cross, but he sent it wide as his side dropped to fourth.
Wigan boss Uwe Rosler:
"We had a game plan and played differently than they expected us to. We decided not to play our passing game and wanted to have a high line and I think it worked very well - we had more attempts on goal and the better chances in the first half.
"The substitution played a part in the goal and it was great individual skill from Beausejour. He's a player we can use in all positions on the left-hand side and he showed today why he is probably going to the World Cup.
"What I didn't like so much was the last 10 minutes when we allowed them to run with the ball and they had two massive chances. Overall, they had more possession but we had more attempts on target and I think we deserved to win the game."
Derby head coach Steve McClaren:
"We were done by a sucker punch and Wigan came to stop us playing and frustrate us. It was going to be one of those games and I said at half-time it would be won or lost on a set play.
"Wigan will say they did a great job on Derby and we have to make sure we pay greater attention to details. But at the end of the day, we've had good fortune over the recent months and won games when maybe we could have drawn or lost so I've got no complaints.
"We didn't do enough to win this game, although I didn't think we deserved to lose it and it's a harsh lesson."
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