Exactly a year to the day since his departure from Reading, McDermott watched his Leeds side follow up Saturday's 5-1 home thrashing at the hands of Bolton Wanderers with another poor Elland Road performance.
Garath McCleary – who struck four times for Nottingham Forest in a 7-3 win at Leeds in March 2012 - capitalised on a defensive mix-up between Jason Pearce and Jack Butland to break the deadlock before Royston Drenthe curled home a fine free-kick.
Nick Blackman and Hal Robson-Kanu put Reading 4-0 up with 35 minutes to play, but Matt Smith and Rodolph Austin were both on target to set up a nervy finish as Leeds at last showed some fighting spirit.
McDermott, though, will be aware that a five-match winless run places extra pressure on him as uncertainty over Massimo Cellino's controversial takeover continues.
Blackpool ended a 17-game winless streak in the Championship with a 1-0 home victory over their former manager Ian Holloway's Millwall side, the first since Barry Ferguson replaced Paul Ince as temporary boss.
Ricardo Fuller's first goal since the end of November – a near-post header – put Blackpool ahead after 14 minutes before Matt Gilks saved Steve Morison's penalty after the Millwall striker had been hauled down in the box.
Leaders Leicester City are eight points clear of nearest rivals Burnley following a 3-0 win at second-bottom Barnsley. Jamie Vardy scored either side of setting up Danny Drinkwater as Nigel Pearson's men edged closer to sealing automatic promotion.
Derby County and QPR endured frustrating evenings in the scramble for the second automatic spot.
Steve McClaren's Derby drew a blank in front of goal for a third game in a row after being held to a goalless draw by Bolton at Pride Park, while late goals from Leonardo Ulloa and Stephen Ward saw QPR lose 2-0 at Brighton and Hove Albion.
Ipswich Town boosted their play-off chances with a 1-0 win at Yeovil Town thanks to Christophe Berra's close-range effort. Nottingham Forest are five games without a league win after drawing 1-1 at Middlesbrough.
Watford were left to rue Mathias Ranegie's moment of madness in their 2-1 reverse at Doncaster Rovers.
Ranegie was given a straight red card for lashing out off the ball at James Husband after 18 minutes and Doncaster wasted little time taking advantage, Chris Brown breaking the deadlock six minutes later.
Ikechi Anya levelled, but up popped Billy Sharp in the last minute to boost Doncaster's survival hopes.
