Wayne Bridge's cross from the left was flicked on towards the back post by Andrea Orlandi where Lopez volleyed home (20), with poor marking from the visitors contributing to their problems.
The game had begun brightly enough but was short on clearcut chances, although Brighton keeper Tomasz Kuszczak was forced to tip a Junior Stanislas ball over the bar.
Keith Treacy then tried his luck with a curling 20-yard effort that went narrowly wide of the mark as Sean Dyche's charges began in positive fashion.
Orlandi headed a whipped corner from Vicente over at the other end before the hosts took the lead against the run of play.
But Burnley rallied and Jason Shackell went close to grabbing an equaliser with a header from Treacy's cross that was kept out by Kuszczak.
Another Shackell header was cleared off the line by Albion midfielder Gary Dicker, before Kuszczak pulled off a superb save with the ball heading for the bottom corner from Dicker's second effort.
Lee Grant was made to work in the Burnley goal though as he kept out a Jose Ulloa chance on his 100th league start for the club.
The Clarets continued to press and Grant McCann hit a half-volley over in the closing stages.
Dean Marney also shot wide after Danny Ings crossed from the byline but Gus Poyet's side held out as they moved back into the play-off places.