Leeds took advantage of Norwich's slip-up at Preston by beating Swansea to return to the top of the championship.
Leeds defender Pontus Jansson marked his 28th birthday with the opening goal on Elland Road, reacting first to Ezgjan Alioski's blocked shot to the bottom corner from 12 yards.
Alioski also provided Leeds' second goal for Jack Harrison, who nodded past Erwin Mulder at his near post a moment after the Swansea goalkeeper had kept his powerful drive.
Oli McBurnie's penalty gave Swansea late hope after Luke Ayling's clumsy foul on Joel Asoro, but Leeds held on to a point clear of Norwich, who lost 3-1 at Deepdale.
Clear Swansea's chances were scarce but just come back when he was half-time when Matt Grimes's free kick kicked the post.
Daniel James, who almost joined Leeds in January, but otherwise he was kept relatively quiet by the hosts' defense before being substituted after 67 minutes.
McBurnie causes some lingering nerves, with Patrick Bamford and Kemar Roofe both going close to extending the home side's advantage.
However, their two first-half goals proved enough to maintain a three-point gap to third-placed Sheffield United.
They have a 10-day break until their next game at home to Bolton on 23 February, while Swansea are in fifth-round FA Cup action on Sunday, when fellow club Brentford visit the Liberty Stadium.
Leeds head coach Marcelo Bielsa told BBC Radio Leeds:
"We deserved to win. It's hard to understand that we just won by one goal because we dominated the game and had many chances.
"The players will have a four-day rest from Thursday until Sunday. We'll take advantage of this period to recover well."