The Seagulls flew in to a sixth-minute lead when skipper Inigo Calderon stooped low to head in a corner from Elliott Bennett.
But Walsall threatened a surprise when their skipper Andy Butler headed his second goal of the season after 11 minutes. Tommy Elphick sliced a clearance high in to the air and the Saddlers defender headed home.
It took Brighton only two minutes at the start of the second half to regain their lead, when top scorer Glenn Murray rising unchallenged to head in his 22nd goal of the season from Bennett's corner.
Any hope Walsall had of saving the game were ended when Emmanuel Ledesma, playing against his former club, was shown a red card for a two-footed challenge on Brighton defender Adam El-Abd.
Brighton were comfortably in control when home goalkeeper Jimmy Walker kept out a drive from Murray, but in stoppage time Bennett burst forward to hammer a right-foot drive which flew past Walker as the Seagulls made it 11 wins in their last 12 games.
Southampton returned to winning ways thanks to Guly Do Prado's late strike saw them win 1-0 at home to Bristol Rovers. Do Prado netted from the edge of the box to keep Saints in second spot.
Joey Gudjonsson boosted Huddersfield's automatic promotion hopes by scoring a late free-kick to claim a hard-earned 1-0 victory at Charlton.
Goalkeeper Joe Lewis was the hero with a last-gasp penalty save as Peterborough produced a super second-half turnaround to beat Plymouth 2-1 and stay in the automatic promotion picture.
Darren Ferguson's men overturned an interval deficit to plunge rock-bottom Plymouth a step closer to relegation, but only after Lewis had brilliantly kept out substitute Luke Summerfield's spot-kick at the death.
Earlier goals from defender Ryan Bennett and star striker Craig Mackail-Smith - who struck his 30th goal of the season - did the trick for a Posh team chasing an instant return to Championship football.
Sean O'Hanlon scored the only goal to keep MK Dons on course for a play-off place and push his former club Swindon ever closer to League Two.
Two goals from top scorer Jamie Cureton kept Exeter's slim play-off hopes alive as they beat Leyton Orient 2-1 at St James' Park.
Colchester's lingering play-off hopes were dashed as Carlisle produced a blistering first-half display of fast attacking football in a 4-1 win at Brunton Park.
Bournemouth claimed their first win in eight games as they won 2-0 at Notts County who endured a club record ninth straight defeat.
Rochdale slipped out of the play-off places after Robbie Simpson`s late winner in a 1-0 win for Brentford.
Tommy Miller scored against his former club to set Sheffield Wednesday on their way to a 2-0 victory over Hartlepool.
The midfielder, who was born in Hartlepool, stepped up to smash home his 10th goal of the season from the penalty spot after Sam Collins was adjudged to have fouled Neil Mellor inside the area.
Gary Madine, who scored a hat-trick for Carlisle against Hartlepool earlier this season, sealed victory with a well-taken 18-yard drive after good work from Jermaine Johnson.
Tranmere boosted their survival hopes with a 2-0 victory over fellow strugglers Dagenham & Redbridge.
Enoch Showunmi had an early goal ruled out for offside but there was no denying the home striker in the 12th minute when he headed in from an Aaron Cresswell cross. Rovers doubled their lead in the 34th minute as Ian Goodison stole in at the far post to head home from a Joss Labadie free-kick.
Andy Welsh struck five minutes from time as 10-man Yeovil held Oldham to a 1-1 draw at Huish Park. Chris Taylor had given the Latics a 17th-minute lead.