Leeds had started two points behind Norwich but goals from Pontus Jansson and Jack Harrison were enough to move it back to the summit.
Oliver McBurnie did pull one back for Swansea with a late penalty but it was too little too late as Leeds sealed an 18th win of the campaign.
Leeds has a one-point advantage over Norwich thanks to stunning display from Preston – managed by former Canaries boss Alex Neil – at Deepdale.
CANARIES KNOCKED OFF THEIR PERCH
Preston quickly opened up a 2-0 lead over Norwich as Ben Davies and Paul Gallagher beat Tim Krul.
Marco Stiepermann missed a penalty before the break and when Sean Maguire scored Preston's third, Norwich was beaten.
Teemu Pukki grabbed a consolation in stoppage time but it was never going to be enough to stop it dropping down to second position following the 3-1 defeat.
Sheffield United is hot on its heels after a 1-0 win over 10-man Middlesbrough, Richard Stearman's first goal of the season enough to move the Blades within two points of the automatic promotion places.
LAMPARD LEFT FRUSTRATED
With Middlesbrough losing, Derby County had the chance to move into the top-six but it could only take a point at bottom club Ipswich Town after a 1-1 draw.
Tom Lawrence gave Derby an early lead at Portman Road but Jon Nolan rescued a point minutes after coming off the bench for Paul Lambert's strugglers.
"The team performance wasn't good enough," said a frustrated Frank Lampard. "If there was a natural complacency from going 1-0 up, then we got taught a lesson."
SMITH LOSES ON BRENTFORD RETURN
Dean Smith's first trip back to Brentford ended in a 1-0 defeat as his Aston Villa side conceded in the 91st minute at Griffin Park, Neal Maupay netting his 18th goal of the campaign.
"We are getting further away [from the promotion picture] at the moment because we're not picking up points," said a dejected Smith. "We have to take stock of it now and make sure we go and get a result against West Brom."
Elsewhere, Reading moved out of the relegation zone with a 2-1 win over Blackburn Rovers, while Stoke City is four games without a win after a goalless draw against Wigan Athletic.