Exactly a year after losing his job at Reading, Leeds manager McDermott responded to his side's 5-1 thrashing against Bolton by making five changes and reverting to using wing-backs.
The kick-off was delayed by half an hour after players, match officials and spectators were delayed by traffic congestion on the M62 motorway.
The Royals were quickly into their stride and Jobi McAnuff was not far wide when Royston Drenthe's blocked shot rebounded to him.
Leeds needed a confidence lift but instead they shot themselves in the foot by gifting the opening goal to Garath McCleary in the 25th minute.
Lithuanian defender Marius Zaliukas, restored to the starting line-up for the first time since Leeds' 6-0 defeat at Sheffield Wednesday in January, played a back-pass which Jason Pearce and goalkeeper Jack Butland left to each other in a communication mix-up.
McCleary was left the simple task of stroking the ball into an unguarded net.
However, the goalscorer was injured soon afterwards and after initially attempting to play on he was replaced by former Sheffield United forward Nick Blackman in the 40th minute.
Hal Robson-Kanu should have doubled Reading's lead shortly before McCleary's departure but his shot from beyond the far post was deflected to safety off Butland.
There were ironic cheers from Leeds fans just before the interval when Alex Mowatt's header tested Alex McCarthy for the first time, the Royals goalkeeper stretching to save under his bar.
But those same fans were demanding to know what was going on when Reading scored three times in rapid succession after the break.
With 47 minutes gone, Drenthe curled a free-kick into the top-left corner from just outside the penalty box.
A minute later Danny Guthrie's free-kick from the left was headed in from six yards by substitute Blackman and in the 54th minute Robson-Kanu's angled shot sped past the bemused Butland.
On the hour, McDermott sent on striker Matt Smith in place of Zaliukas and four minutes later Pearce headed down a high ball for the new arrival to stab home at the far post.
A minute later Rudi Austin found the top-right corner of Reading's net with a spectacular 30-yard drive, to offer his manager a glimmer of hope with Reading's lead halved.
Smith was a fraction away from connecting with a goalmouth header and seconds later he was thumping the turf in frustration after glancing a header agonisingly outside the far post, but Leeds had left it too late.