Despite a brace of goals by Didier Drogba, Chelsea were pegged back, first by Leroy Lita and finally and cruelly by an own goal from Michael Essien.
Already without regular goalkeepers Peter Cech and Carlo Cudicini, Chelsea were also without John Terry, Joe Cole and Arjen Robben.
However despite this, Chelsea started brightly and within four minutes Frank Lampard just missed with a fine left-foot shot from just outside the six-yard box.
On nine minutes Glen Little showed why he was such a threat down the left by pulling Paulo Ferreira out of position on this occasion.
Reading keeper Marcus Hahnemann was quick off his line to smother a right footer by Drogba on 14 minutes and seconds later Salomon Kalou blasted the ball high over the Reading goal.
Reading had two corners in the first 15 minutes and both times Chelsea dealt with them confidently.
On 23 minutes Essien attempted to reproduce his wonder goal against Arsenal but this time his 30-yard drive was embarrassingly wide.
Hahnemann pulled off another excellent save by pushing clear a goal-bound header from Drogba on 29 minutes and seconds later he was happy to see an Essien long-range flyer drift wide.
Drogba was desperately unlucky not to score on 36 minutes when his deft right-foot shot was deflected past the post.
From the resulting corner though he rose to nod the ball home from just inside the six-yard box ahead of the otherwise impressive Hahnemann.
An early second-half strike from Andriy Shevchenko went high and wide from the unimpressive Ukraine international
Reading's best chance of the game came on 55 minutes when Ricardo Carvalho almost toe-poked the ball into his own net, but had the Portuguese international not got a touch it would have let in Kevin Doyle.
A minute later and Reading signalled their intent to attack Chelsea and Steve Sidwelll flashed a right-footed drive past Henrique Hilario's right-hand post.
Shevchenko was eventually substituted on 57 minutes for Shaun Wright-Phillips and his first touch came five minutes later when his right-wing cross eluded Drogba.
Another sweeping counter attack from Chelsea saw Kalou once again shoot high over the bar.
Reading got their reward for their positive approach when Little advanced to the edge of the Chelsea area moments later and his deep cross was met by the diving head of Lita.
Jose Mourinho rang the changes, sending on John Obi Mikel and Ashley Cole and this seemed to settle the champions as they regained their lead on 72 minutes.
Drogba was once again the hero, latching on to a Wright-Phillips' cross and heading home from eight yards to squeeze the ball between Hahnemann and the keeper's right post.
Reading pushed forward and could have equalised when Doyle saw a snap-shot go inches over the Chelsea bar from eight yards out on 77 minutes.
Chelsea, struggling without captain Terry, nearly surrendered their lead when Sidwell produced an unchallenged header which went just wide of Hilario's goal.
But the equaliser wasn't long in coming and substitute Cole's first telling contribution was to send the ball crashing on to the body of Essien when attempting to clear and it ricocheted off the midfielder and into the net for a fully deserved Reading goal.
Chelsea failed to produce the guile necessary to get yet another last minute winner and Mourinho's side were forced to settle for a point.