Hosts Reading controlled large parts of the opening 45 minutes although Saints goalkeeper Kevin Davies was rarely called into action.
When they did create an effort, Mikele Leigertwood's effort from distance was tipped over the bar by Davies.
However, central midfielder Leigertwood was not to be denied and he finally broke the deadlock after 70 minutes. Jobi McAnuff struck the foot of the post but Leigertwood reacted quickest to convert the rebound from a narrow angle.
The situation deteriorated further for Nigel Adkins' side when captain Dean Hammond was handed his marching orders for a foul on McAnuff in the 76th minute.
The Saints rallied without their skipper though and with ten minutes remaining they were level. De Ridder had only been on the pitch a matter of minutes when he wriggled free of two defenders before sending his effort into the roof of the from close range.
Reading substitute Jimmy Kebe forced a save from Davies late in the game, but in the end both sides had to settle for a point.