Toronto - French underdog Jeremy Chardy sprang a post-Olympic surprise on third-seeded countryman Jo-Wilfried Tsonga with a 6-4, 7-6 (7/4) defeat on Wednesday to reach the third round of the Toronto Masters.
Chardy, ranked 47th, was playing for the second day in a row while Tsonga was making his first start since losing last week's London Olympics quarter-final against Novak Djokovic.
French 14th seed Richard Gasquet opened with a victory over Mikhail Kukushkin of Kazakhstan 6-3, 7-5.
Tsonga was the day's most notable early victim of Olympic fatigue as the ATP schedule hits a run of two straight weeks of 1000-point events before the start of the US Open on August 27.
For Olympic participants, this week marks a return to North American hardcourts after neary five months on clay and grass.
London bronze medallist Juan Martin del Potro, the Argentine sixth seed, went out to Czech Radek Stepanek 6-4, 7-6 (7/5).
"I came here Monday night, many players pulled out from here," said the fatigued South American who looks likely to head straight home for some rest. "It's not easy to play after a big effort in the Olympics, but I tried anyway.
"Now I need time to recover my body if I want to stay healthy."
Del Potro, a former US Open winner, wants to regain his full powers on court before the start of the final major of what has been a busy season. "This was my first match on hard courts since Miami (March).
"But now I will have time to relax, to train, and I will be 100 per cent for the next tournaments and 100 per cent for my favourite tournament in New York."
In other results as seeds went into action after byes into the second round, No 5 Serb Janko Tipsarevic defeated Russian Mikhail Youzhny 7-6 (7/2), 6-4 while Croatian Marin Cilic, the tenth seed, beat Marcos Baghdatis from Cyprus 7-5, 6-3.
Latest results from the third day of the ATP Toronto Masters on Wednesday (x denotes seeding):
Marcel Granollers (ESP) bt Florian Mayer (GER x15) 6-3, 6-4
Marin Cilic (CRO x10) bt Marcos Baghdatis (CYP) 7-5, 6-3
John Isner (USA x8) bt Pablo Andjar (ESP) 7-6 (7/5), 7-5
Milos Raonic (CAN x16) bt Viktor Troicki (SRB) 6-3, 6-4
Radek Stepanek (CZE) bt Juan Martn Del Potro (ARG x6) 6-4, 7-6 (7/5)
Janko Tipsarevic (SRB x5) bt Mikhail Youzhny (RUS) 7-6 (7/2), 6-4
Jeremy Chardy (FRA) bt Jo-Wilfried Tsonga (FRA x3) 6-4, 7-6 (7/4)
Richard Gasquet (FRA x14) bt Mikhail Kukushkin (KAZ) 6-3, 7-5
Philipp Kohlschreiber (GER x12) bt Fabio Fognini (ITA) 6-2, 6-2