Leeds United needed an 89th-minute strike from Pablo Hernández to snatch a 1-0 win over promotion-hopefuls Swansea City and inch closer to the Championship title.
Marcelo Bielsa's side entered the game level on points with West Bromwich Albion, with Brentford just three points behind and breathing down their necks.
Swansea looked liveliest early on and were perhaps unlucky not to take the lead. Chelsea loanee Conor Gallagher looked lively and dangerous throughout and came close to opening the scoring, as did Liverpool's Rhian Brewster.
It took Leeds about half an hour to wake up but they were almost handed the lead by Ben Cabango, whose lapse in concentration presented Patrick Bamford with an excellent chance, only for the Leeds man to fire a tame shot right at Freddie Woodman.
As the game progressed, tensions began to boil over. Both teams knew how important a victory was, so they started racking up yellow cards as the game turned scrappier with each passing minute.
Bielsa made the decision to send on former Swansea man Hernández at the break, but he initially struggled to get into the game. Just like the first half, Swansea began on top and Gallagher influenced proceedings far too much for Leeds' liking.
Hernández's impact was first felt around the hour mark as he set up Jack Harrison for a volley which found its way to Bamford, whose header forced an excellent save from Woodman.
Swansea thought they had won it in the 80th minute as Connor Roberts fired home, but his effort was eventually ruled out after André Ayew was found to be offside during the build-up.
It was Leeds who had the last laugh, however, as Hernández came back to haunt his former side with an 89th-minute dagger.
His scrappy effort from inside the area trickled past Woodman and into the back of the net via the post, sending the visitors wild and moving them three points clear at the top of the table with three games to go.
Perhaps most importantly for Leeds, they now sit six points clear of third-placed Brentford, meaning an automatic promotion spot is all but ensured. With meetings with bottom-side Barnsley, Derby County and Charlton Athletic coming up, Bielsa's men will know it is their title to lose.
As for Swansea, they missed the chance to climb back into the top six and instead remain one point behind Cardiff City. Steve Cooper's men must now pick themselves back up and prepare for a trip to Nottingham Forest on Wednesday.