Reading moved top of the Championship after Adam Le Fondre's late double broke the resistance of 10-man Leeds.
In a feisty first half, Leeds had Zac Thompson sent off after 13 minutes for a rash tackle on Jobi McAnuff.
The visitors frustrated Reading and went close when Ross McCormack's shot hit the outside of the post and Robert Snodgrass wasted a gilt-edged chance.
But Le Fondre chested in Hal Robson-Kanu's nod across goal after 84 minutes and sidefooted in for Reading's win.
It was a hard-fought success for Brian McDermott's side against a Leeds team who resisted resolutely for the most part and whose play-off hopes are now all but over.
Reading, on the other hand, only enhanced their automatic promotion credentials with a seventh home win on the trot as they inflicted the first away defeat Leeds boss Neil Warnock has suffered since taking over the Elland Road club.
Warnock had highlighted the depleted nature of his side because of injuries and suspensions leading up to the game and it did not take long for the visitors to suffer another setback when Thompson was sent off.
Reading had gone close with headers from Noel Hunt and Kaspars Gorkss before Thompson, 19, flew into a tackle on winger McAnuff to get his marching orders.
Former Leeds defender Ian Harte showed little sentiment as he went close with a long-range shot before a left-wing cross inadvertently came off the far post.
Leeds nearly made their predicament worse but Danny Pugh escaped a red card for a studs-first tackle on Jem Karacan.
In a first half of eye-watering tackles rather than eye-catching football, Karacan eventually hobbled off after a Michael Brown challenge proved the final straw for him.
With the home side failing to make their numerical advantage count, McCormack fired a shot against the outside of the post before Snodgrass had an even better chance.
The Leeds captain had a clear sight of goal only to sidefoot too close to Royals keeper Adam Federici, who parried the shot away.
The miss proved crucial as Reading heeded the warning and went up the other end to score when Jimmy Kebe's cross was nodded back across goal by Robson-Kanu and Le Fondre, who had a goal disallowed for offside minutes earlier, was in the right place to provide the finishing touch.
Le Fondre slotted in a second when he benefited from good work from Jason Roberts as Reading leapfrogged Southampton, who play their game in hand on the Royals against Portsmouth on Saturday.