Lucie Safarova's return to the WTA Tour proved disappointing as the world number seven suffered a straight-sets defeat to Andreea Mitu in the WTA Generali Ladies Linz.
The top seed in Linz after recovering from a bacterial infection that saw her hospitalised for a week, Safarova was unable to make it through her first match - going down 6-3 6-4 to the world number 95.
Mitu charged into a 3-0 lead in the opener and broke Safarova again after the Czech had atoned for her early loss of serve.
The second set went with serve until the seventh game, despite both players coming under pressure, but Mitu then broke for a 4-3 lead before holding on two occasions to set up a second-round tie with Anna-Lena Friedsam.
Safarova said: "It wasn't the best performance from me, but for a first match after so long, it wasn't that bad.
"I'm thankful that I'm back on the court; that's very positive because 10 days ago I was still in bed, so it's pretty good to be back here again."
There was another shock late in the day as fourth seed Andrea Petkovic threw away a 4-2 lead in the final set to be beaten by Johanna Larsson.
A dramatic finale saw Petkovic register the only hold of serve in six games at the start of the deciding set.
However, Larsson fought back superbly, reeling off the next four games to triumph 3-6 6-3 6-4.
Camila Giorgi, Anastasia Pavlyuchenkova and Barbora Strycova, the respective sixth, seventh and eighth seeds, progressed to round two with victories over Julia Goerges, Katerina Siniakova and Barbara Haas.
Giorgi triumphed 6-3 6-4, Pavlyuchenkova routed her opponent 6-0 in the second set after being taken to a tie-break in the first and Strycova won the opening seven games of her match only for Haas to fight back and force a decider, which the favourite won 6-4.
The in-form Johanna Konta capitalised on her late entry as a lucky loser by thrashing Annika Beck 6-1 6-3, while there were also wins for Madison Brengle, Mona Barthel, Alison van Uytvanck, Denisa Allertova and Stefanie Voegele.