West Brom surrendered top spot in the Sky Bet Championship after being held to a 0-0 draw at Swansea.
Slaven Bilic's side failed to find a first-half breakthrough before being put on the back foot for large spells of the second period to allow Leeds to steal a march at the league summit.
Jay Fulton missed a pair of gilt-edged chances that could have given the Swans a valuable victory in the race for the playoffs, but after QPR's victory at Preston, they closed the gap on the top six to three points.
West Brom had former Swan Kyle Bartley and midfielder Romaine Sawyers back in the starting XI in place of Ahmed Hegazi and Rakeem Harper as they made two changes from their last Championship outing.
Aldo Kalulu was brought in as the only change to the Swansea side that drew at Blackburn last weekend after Jordan Garrick was struck down by illness on Friday night.
Only six substitutes were listed on the bench by manager Steve Cooper due to a lengthy injury list, loan restrictions and an outbreak of mumps within the under-23 squad.
For all of West Brom's early dominance, it was Swansea who carved out the best chance of the first 20 minutes after Rhian Brewster nodded a long ball back into the path of Kalulu.
The Liverpool loanee sprinted into the box while the ball was being worked to Andre Ayew on the left flank and would have tucked his cross away if it was not for an intervention from former Swan Bartley.
Ayew then got in the way of a Brewster effort, but from that point on Bilic's men cranked up the pressure to send the Swans further back into their defensive shell.
Hal Robson-Kanu was half a yard away from getting on the end of Callum Robinson's whipped ball, before Matt Grimes lost concentration for a split second.
The Swans midfielder gifted possession to Robinson who fired a low shot towards goal, but Freddie Woodman got a strong hand to the ball to parry the danger away.
After managing to survive until the half-time whistle, the hosts should have been ahead 40 seconds into the second period.
Grimes fired a shot from 25 yards that was parried into the path of Fulton, but the midfielder sliced the rebound over the bar from 12 yards.
He found the stands instead of the net again with another great chance after Sam Johnstone tripped Conor Gallagher on the edge of the area. Grimes pulled a low cross back for Fulton, but he blazed over again.
After spending large spells defending their own box, West Brom surged forward in search of a late winner.
The best chance fell to Jake Livermore, but the midfielder fired over from 12 yards out to ensure the game ended goalless.
