TORONTO Aug 6 (Reuters) - Venus Williams got off to a flying start in her return from a two-month layoff but her game quickly fell apart as the seven-times grand slam champion slumped to a 0-6 6-4 6-2 loss to Kirsten Flipkens in the Rogers Cup first round on Tuesday.
Seeds Maria Kirilenko (11) Jelena Jankovic (15) and Ana Ivanovic (16) also had first round wins.
In the second round, Slovak Dominika Cibulkova upended eighth seed Angelique Kerber of Germany 6-7(0) 6-2 7-5 and second seed Agnieszka Radwanska of Poland won 6-2 6-3 over Belgium's Yanina Wickmayer.
Williams, who has played sporadically this season due to a back injury and had not competed since losing in the first round of the French Open in late May, started in fine form on Tuesday but gradually fell apart as the contest wore on.
The five-times Wimbledon champion's serve was slower than usual, her ground strokes were erratic and she seemed slow to the ball as Wimbledon semi-finalist Flipkens consistently changed angles on her.
"I just really started serving a lot more in the last week, so I'm not really 100 percent on the serve yet," the 33-year-old Williams said.
"So it was better not to take too many risks and just do something I felt more comfortable with. This week I will definitely be practicing my serve a lot more and getting more confident in it."
Williams has also been battling an auto-immune disease for the past few years and said she might have come back a week too early. But she feels she needs matches before the US Open, which begins in a little less than three weeks time.
"Coming back from injury, you have to build the confidence to just realize that you can come back and play without pain," she said. "So I feel like I'm in that threshold of building confidence.
"That's a lot of what happened to me at the French (Open), too. I played an intense and a really exciting match, but I hadn't played any matches. So it was a tough situation to be in. Do you play or you don't play? So I feel like in that situation now going into the US Open."
Cibulkova, who won the Stanford title late last month, needed nearly three hours to overcome German Kerber, fighting back from 1-4 down in the third set to seal victory.
"You have to go for it," Cibulkova said. "Then when you make some mistakes, then you get a little bit nervous. It was really long match because we had long rallies and I was the one who was making her run. I think it's normal that she became tired."
Top seed Serena Williams will play her opening match on Wednesday against Italy's Francesca Schiavone. (Editing by Peter Rutherford)