Serena Williams beats Flavia Pennetta in Toronto

Serena Williams, of the United States, reacts to a point on her way to defeating Flavia Pennetta, of Italy, at the Rogers Cup tennis tournament Tuesday, Aug. 11, 2015, in Toronto. (Frank Gunn/The Canadian Press via AP)

TORONTO — Top-ranked Serena Williams rebounded to beat Italy’s Flavia Pennetta 2-6, 6-3, 6-0 on Tuesday in the second round of the WTA Tour’s Rogers Cup.

“I was really frustrated with how I was playing,” Williams said. “And then I got really angry. … So I said, ‘Serena, you’re going to have to be positive and be good to yourself out here.'”

The 21-time Grand Slam winner won a day after sister Venus Williams was eliminated in straight sets by Germany’s Sabine Lisicki.

The 33-year-old Williams blamed unforced errors for her early struggles.

“It was a good opportunity for me because I haven’t played a match on hard courts since April-ish, early, early April, after Miami,” Williams said. “It was a long time ago. So I think it was really good for me to have that match play.”

Williams won the first of her three Toronto titles in 2001.

“Like a nice vintage wine, Williams said. “A good vintage red wine, I’d say, getting better with age, I hope.”

Slumping Canadian star Eugenie Bouchard dropped out, falling 6-0, 5-7, 6-2 to Switzerland’s Belinda Bencic in a first-round match. Bouchard has also lost 13 of her past 15 matches.

“It’s easy to let yourself get negative when you lose a couple of matches in a row or you know your body’s not feeling great,” Bouchard said. “It’s definitely been a tough road. And I feel like I’m at least not going downwards anymore. I’m trying to go on the right path.

“I feel like I can be close to performing well on the court, and it’s just been a long, patient kind of battle, and I feel like I’m close to turning it around.”

On other first-round matches, France’s Alize Cornet upset ninth-seeded Carla Suarez Navarro of Spain 6-3, 6-7 (2), 6-4; qualifier Mirjana Lucic-Baroni of Croatia beat 10th-seeded Karolina Pliskova 3-6, 7-6(5), 6-2; No. 11 Ekaterina Makarova of Russia topped American qualifier Anna Tatishvili 6-3, 6-3; and American Alison Riske defeated 12th-seeded Timea Bacsinszky of Switzerland 3-6, 7-6 (4), 7-6 (3).

Belarus’ Victoria Azarenka beat Ukraine’s Elina Svitolina 6-1, 6-4, and Germany’s Angelique Kerber beat Japanese qualifier Misaki Doi 6-0, 6-1.