Graham Alexander hailed his side's "great win" after they beat Portsmouth 1-0 at Fratton Park to climb to second place in the table.
Jamille Matt scored a scrappy 67th-minute winner to lead Alexander's in-form side to a fourth successive victory.
Delighted Alexander said: "We had to work hard for that win. It was a great result and we might have scored a couple more.
"I thought we were terrific across the pitch and thoroughly deserved it.
"Matt is claiming the goal, but is was messy. He made a great run, held off the centre half and got it in.
"There were other occasions when we might have scored but we had to make sure we were defensively solid.
"Pompey have got some top strikers, like David Connolly, and it was important we kept things tight."
Record signing Matt came close to giving the visitors a first-half lead when his shot rattled home goalkeeper Sullivan's upright.
Matt went one better 23 minutes from time after racing onto Junior Brown's threaded through ball.
Striker Matt's shot struck Sullivan and Pompey defender Sonny Bradley could only help the ball into his own net as he tried to scramble it clear.
Effective on the counter-attack, Fleetwood deserved their sixth win in eight matches.
Pompey mustered only one shot on target in the entire 90 minutes as the early-season promotion favourites slumped to their third defeat of the campaign and their third in four home games.