Andy Murray suffered his first defeat in nearly three months on Thursday when he was beaten by Latvia's Ernests Gulbis in the third round of the Rogers Cup.
Playing just his second match since winning Wimbledon, Murray fell 6-4 6-3 in less than an hour and a half in one of the key lead-up events to the U.S. Open.
The 24-year-old Gulbis, ranked 38th in the world, produced some breathtaking shot making and deft touches while Murray struggled to produce his best on the Montreal hardcourts.
Gulbis will now face either Argentina's Juan Martin Del Potro or Canadian Milos Raonic in the quarter-finals while Murray will head to Ohio for next week's Cincinnati Masters.
Rafa Nadal, also back in action for the first time since Wimbledon, was given a tough workout from Poland's Jerzy Janowicz but survived to win 7-6 6-4.
Janowicz served for the set and led 3-0 in the second but was unable to capitalise on his chances as the Spaniard clawed his way back.
"It was a very good victory against a very difficult opponent," Nadal told reporters.
"He played a little up and down but I'm pleased with the way I played...it's a great victory for me."
Nadal's next opponent is Australian qualifier Marinko Matosevic, who celebrated his 28th birthday with a 7-6(7) 6-7(10) 6-3 victory over Benoit Paire of France.
Later on Thursday, world number one Novak Djokovic was scheduled to meet Uzbekistan's Denis Istomin for a place in the last eight.