Stoke are still searching for their first win of the Championship season following a 2-1 defeat at home to Bristol City.
It had looked like it could finally be Stoke's day after Sam Clucas slotted home from a fourth-minute corner.
But Stoke, who remain rooted to the foot of table, tired after the restart as Bristol made their man advantage count.
Clucas got Stoke off to a perfect start when he smashed home following a good lay-off by Bruno Martins Indi.
But the game turned on its head when Allen was sent-off for going in with his studs on Brownhill.
Han-Noah Massengo had to turn the ball over his own crossbar for a 19th minute corner as the Potters continued to dominate.
Bentley spread himself brilliantly two minutes later to keep out a close-range effort from McClean.
Jack Butland saved with his feet to keep out an Andreas Weimann shot after 23 minutes as the game burst to life.
Tommy Rowe was unable to find the target with a header from Brownhill's cross on 30 minutes.
Antoine Semenyo blazed over from a tight angle after 42 minutes, before Clucas failed to keep a long-range effort down on the stroke of half-time.
Tom Ince saw a shot saved by Bentley on 48 minutes after a surging run into the box.
Badou Ndiaye dragged an effort wide from distance minutes later as the home side looked for a decisive second.
But Diedhiou headed home from the goal-line after a brilliant cross by Jack Hunt on 55 minutes to drag Bristol level.
The visitors were ahead seven minutes later when Edwards turned into his own net while under pressure.
But Hunt again deserved all the credit for the goal after he beat his man before delivering another deadly chipped cross to the back post.
Stoke were then unable to create a good chance to level in the closing stages with an off-target volley from Clucas the best they could offer.