The ATP Montreal Masters suffered another major blow Wednesday as its top two seeds exited the tournament within hours of each other, with Germany's Alexander Zverev stunned in the second round and Canadian Felix Auger-Aliassime forced to withdraw because of injury.

Top seed and world No. 3 Zverev, the reigning French Open champion and Wimbledon runner-up, was upset by Dutchman Tallon Griekspoor, who rallied for a 6-7 (3), 6-2, 6-4 victory in the second round.

"I didn't expect to play well," Zverev said. "I also didn't expect to play this bad, to be honest."

Montreal native Auger-Aliassime withdrew ahead of his scheduled night match after suffering a back injury during a training session Monday.

"It was quite sudden. I was training here for two weeks and I had zero problems," Auger-Aliassime said. "Just the timing is tough.