Leeds suffered a dismal return to action as the Championship promotion contenders lost 2-0 at Cardiff on Sunday in their first match since the coronavirus lockdown.
Marcelo Bielsa's side are hoping to win automatic promotion to the Premier League after losing in the play-offs last season.
A victory in south Wales would have given them a 10-point lead over third placed Fulham, with the top two going up automatically.
But Junior Hoilett and Robert Glatzel scored in either half for play-off hopefuls Cardiff to deny Leeds the chance to return to the top of the table.
Second placed Leeds are behind leaders West Bromwich Albion on goal difference.
Fulham are seven points adrift of Leeds with eight games remaining in the second-tier promotion race, keeping Bielsa's men firmly in control of their own destiny.
Leeds' best chance came when Cardiff's Dion Sanderson put a poor back pass out for a corner.
Luke Ayling headed the resulting delivery towards goal, forcing Will Vaulks into an acrobatic clearance yards from his own goal.
It was against the run of play when Cardiff took the lead in the 35th minute.
Kalvin Phillips gave the ball away in midfield and Hoilett picked up possession and drove towards goal.
His left-foot shot from distance beat Illan Meslier, who should have done better.
Hoilett celebrated with a Cardiff shirt sporting the name of Peter Whittingham, the former Bluebirds midfielder who died in March.
Cardiff introduced Glatzel and Nathaniel Mendez-Laing for Paterson and Albert Adomah and the two substitutes made an immediate impact to double Cardiff's lead.
Leeds captain Liam Cooper gave away possession to Mendez-Laing and he passed inside to Glatzel, whose shot went in off the post.
Leeds manager Marcelo Bielsa