Crystal Palace lost valuable ground in the Championship's promotion race as they were held at home by Reading.
In an open match, Palace thought they had taken the lead when Glenn Murray slotted home only to be denied by a marginal offside call.
Reading, unbeaten since 10 September, went close when Noel Hunt's header from Jimmy Kebe's cross hit the post.
And Kaspars Gorkss had a last-minute header ruled out for the visitors for pushing an opponent.
For Reading, the result was their fourth draw in five matches yet had it not been for Palace keeper Julian Speroni they might have collected all three points.
Jem Karacan saw an early effort well saved by Speroni while the keeper had to make a superb stop to thwart Karacan's 20-yard drive later in the half.
Palace thought they had taken the lead five minutes before the break when Murray latched on to Williams' through-ball and beat Adam Federici, only to be denied by the assistant's flag.
Reading, looking to move into the top half of the table, should have been ahead in the second half but Hal Robson-Kanu headed Jobi McAnuff's cross wide from close range.
Federici made a good save from Mile Jedinak as Palace pressed but the visitors again went close when Hunt headed against the post with Speroni beaten.
And in the final minute Karacan cleared off the line for Reading before Gorkss was denied at the other end because of a push.