Slovakia's Daniela Hantuchova was knocked out of the Swisscom Challenge at the first hurdle after a 7-6 7-5 defeat to Argentina's Paola Suarez on Tuesday.
Eighth-seeded Hantuchova, who returned from a brief lay-off after an ankle problem last week, lost out in a tight first-round encounter as the experienced Suarez triumphed.
Suarez, 27, gained the early initiative as she got the better of her 20-year-old opponent in comfortably winning the first set tiebreak 7-2.
Hantuchova broke in the first game of the second set, but Suarez levelled again and went on to break the Slovakian's serve once more when leading 6-5 to complete the victory.
Switzerland's Patty Schnyder began the defence of her title with a dominant 6-3 6-3 victory over Eleni Daniilidou.
Schnyder, backed by her home crowd, was never troubled in the opening set as a single break proved enough against a player she defeated in the French Open earlier this year.
Greek Daniilidou then faltered after being broken in the second set and Schnyder produced a forehand winner to close out the victory the Swiss crowd had come to see in 68 minutes.
The world number 18, who beat Lindsay Davenport in last year's final, faces a tricky second round game against third seed Amelie Mauresmo of France.
ABDOMINAL INJURY
Frenchwoman Mary Pierce was forced to forfeit her first round tie with Katarina Srebotnik due to an abdominal
Wild card entry Pierce, competing with a heavily strapped thigh, went off court twice for treatment on the injury in the first set, which she lost 6-0 to the 22-year-old Slovenian.
Pierce was then broken a fourth successive time to go 2-0 down in the second set and decided to retire from the match.
The 28-year-old, once ranked third in the world, has suffered a spate of injuries over the past three years.
"My body isn't used to playing at a higher level at the moment," she said. "My body needs to recover and get used to this level again. I'm not feeling right yet."
Pierce said she plans to take two weeks rest before completing her season in Quebec.
Srebotnik, who came through three qualifying rounds, will now face top seed and world number one Kim Clijsters.
Belgian Clijsters comes into the Zurich tournament on the back of her victory in the Filderstadt Grand Prix in Germany on Sunday when she defeated compatriot Justine Henin-Hardenne.
In Tuesday's opener, Russian Elena Bovina, a semi-finalist in Filderstadt, continued her fine run of form as she disposed of Australian Alicia Molik 6-4 6-1 and will now meet Suarez.
Russian Nadia Petrova comfortably overcame Swiss wild card Marie-Gaiane Mikaelian 6-3 6-1 to set up a clash with compatriot Elena Dementieva, the fourth seed.
