Montreal - Angelique Kerber's first match since capturing the Wimbledon title ended in defeat on Wednesday as the German lost 6-4, 6-1 to Alize Cornet of France at the Montreal WTA event.
World No 4 Kerber committed 32 unforced errors against the 34th-ranked Cornet in her 85-minute second round loss.
Cornet, 28, goes on to face Ashleigh Barty of Australia in the third round.
It was her second successive victory against Kerber having also triumphed on hard court in Beijing last year.
Results of the WTA tournament in Montreal on Wednesday (x denotes seeded player):
Alize Cornet (FRA) bt Angelique Kerber (GER x4) 6-4, 6-1
Ashleigh Barty (AUS x15) bt Alison Van Uytvanck (BEL) 7-6 (9/7), 6-2
Carla Suarez Navarro (ESP) bt Lesia Tsurenko (UKR) 6-4, 3-2 - retired