Serena Williams remains on course to retain her French Open title, but was not at her brilliant best against home hope Kristina Mladenovic
Defending champion Serena Williams was left frustrated by her performance as she secured a place in the last 16 of the French Open with a 6-4 7-6 (12-10) victory over Kristina Mladenovic.
The top seed, who is aiming for her 22nd grand slam title, looked laboured at times against the French number one in a match interrupted by rain for two-and-a-half hours.
But while the 34-year-old readily admitted that she had not been at her best, she felt that Mladenovic deserved credit for her battling display.
"I feel like I made a tremendous amount of errors," she said. "But, you know, I feel like she kind of forced me to.
"She forced me to go for it and unfortunately, I wasn't hitting great. It was definitely a challenge for me, obviously.
"I had opportunities to end it a lot sooner and I didn't, but that's also something that I can try to do, you know, going forward."
Williams went on to identify her inability to convert break points as one of her major frustrations during the round-of-32 clash.
"I think in general I definitely didn't play my usual game," she said.
"And some of those break points, most of them I should have won and I didn't.
"Lately I have been really converting those break points, but, you know, I have got to focus on the positives, I guess."
Williams will face Elina Svitolina in the next round after the 18th seed defeated Ana Ivanovic.