Jankovic suffered problems with her wrist and knee during her defeat
Jelena Jankovic saw her 12-match winning streak come to an end as Flavia Pennetta beat her 5-7 6-3 6-3 in the second round of the Zurich Open.
Jankovic, who won three straight titles before the tournament, appeared to hurt her left wrist late in the first set.
She also called for a trainer to treat her bleeding right knee in the second.
The deciding set went with serve until Pennetta hit a backhand winner to lead 5-3, and with two points for the match, she wrapped up victory with an ace.
It was the Italian's first victory over Jankovic in six meetings, having lost in straight sets to the Serb in Moscow last week.
"Last week I didn't have a lot of luck and today I was more aggressive," Pennetta said.
Jankovic, who will play her final tournament of the season at the WTA Tour championship in Doha, Qatar, from 4-9 November, said she was tired from her recent schedule.
"I didn't have any gas in the tank," she said. "I am not a machine. Flavia took advantage, she was the better one today."
Elsewhere, Victoria Azarenka of Belarus whitewashed Monica Niculescu of Romania 6-0 6-0. Niculescu, while 18-year-old Czech Petra Kvitova beat fellow qualifier Sofia Arvidsson of Sweden 6-2 6-1.