Julio Arca deservedly put the Black Cats ahead in the 52nd minute with his seventh goal of the season only for Dave Kitson to strike twice in a six-minute spell to turn the form book upside.
The Black Cats would have equalled a post-war club record of nine successive victories had they been able to hang to a deserved lead, but the introduction of veteran striker Les Ferdinand midway through the second half changed the face of a game the home side should have wrapped up by the interval.
But they were kept at bay by an inspired goalkeeping display from Marcus Hahnemann, woeful finishing and bad luck when a Carl Robinson header came back into play off the bar just before the interval.
From the second minute when Gary Breen flashed a header just past the post from a Liam Lawrence corner, Sunderland called the tune in a one-sided first half.
Marcus Stewart was inches away from making contact to an Arca through ball and Hahnemann saved well from Robinson. A great turn and run at goal by Chris Brown went unrewarded and Arca's low drive was well saved at the foot of the post.
Hahnemann again saved well from Arca as Reading relied totally on defence apart from the odd foray into the home half. Steve Sidwell's close-range effort sailed over the bar, Paul Brooker fared no better with a header and Thomas Myhre saved an Ibrahim Sonko header.
Myhre was replaced by Northern Ireland international Michael Ingham at the start of the second half after suffering a back injury but Sunderland continued where they left off with Arca surging into the penalty area only to be denied by Hahnemann.
But the Argentinian gave Sunderland a 52nd minute lead. Ivar Ingimarsson failed to clear enabling Marcus Stewart to centre for Dean Whitehead to flick on and the lurking Arca to head home at the far post.
Kitson headed straight at Ingham but Reading became a more potent force after the introduction of Ferdinand. He wasted no time in causing Gary Breen and Steve Caldwell problems in the air and it was his 76th minute flick which enabled Kitson to bundle a way through and force an equaliser.
Six minutes later Sidwell looked offside as he cut in from the left and when the chasing Jeff Whitley clipped his ankles from behind, the referee had no hesitation in awarding a penalty.
Kitson kept his nerve to leave Ingham helpless from the spot kick, to the delight of the Reading fans behind the goal whose long journey to the North East had started at 4am.
Sunderland manager Mick McCarthy's response was to thrown on 37-year-old Brian Deane for a belated debut, but apart from Dean Whitehead heading past the post and sending a free-kick over and Arca firing weakly at Hahnemann, there was no way back.
McCarthy, however, remained upbeat and can still see the finishing line in sight despite the latest setback.
"Nobody can go away and say we took our eye off the ball or took our foot off the pedal,'' he said. "For 75 minutes we were terrific and there was lots of reasons why we didn't score.
"We chased the game from the start and perhaps we had too much possession, became hurried and not clinical. On a different day it might have happened and if that's the case we have to make sure it doesn't happen again.
"We can't sit and say what might have happened. Their goalkeeper was inspired and I can assure you it was not lack of concentration. We have played very well and nobody thought it was all over.
"It was always going to be a big game but we are still in the best position. We should have got something out of the game, we didn't, and it's time to move on.''
Reading boss Steve Coppell thought the introduction of Ferdinand and Martin Keown turned the game in his side's favour as they recorded their first back-to-back wins of the year.
"Two years ago Les would have been an automatic choice of nearly any team in the country,'' he said. "I have to decide whether to start with him or bring him on as a substitute as he can be so positive.
"Martin's mentality and drive is vital, that was one of his first games for us and his first victory. And having two experienced players like that coming on helped to change the course of the game.
"The Stadium of Light is an intimidating place to come to. It's the first time I have been here and it's a place where questions are asked. But we got the bit between our teeth after going a goal down after previously looking liking lambs to the slaughter.
"Before the game we had nothing to lose as everybody thought it was another automatic three points for Sunderland. But we got the three points and that's fabulous but it's pointless if we lose our next game.''
Man of the match. Marcus Hahnemann.
The American goalkeeper kept Sunderland at bay throughout a one-sided first half and but for his heroics there would have been no late fightback or three crucial play-off points.