LONDON -- Two down, five to go.
Serena Williams won again at Wimbledon on Wednesday, advancing to the third round as she tries to win a calendar-year Grand Slam.
Williams beat Timea Babos 6-4, 6-1 on Centre Court. The 20-time major champion has already won the Australian Open and the French Open this year. If she can win the last two majors, she would become the first player to win a true Grand Slam since Steffi Graf in 1988.
"Obviously [the Grand Slam] is on my mind, but I would have to win in a really tough draw here, and I would have to win the Open," Williams said. "That's not really easy. You know, obviously it's something I want to do. But at the end of the day, there's a reason it's rarely done."
Two more wins, and Serena will meet sister Venus in Wimbledon's fourth round.
"She poses a big threat for me," Serena said.
Serena's next opponent is Heather Watson, Britain's No. 1 player.
"I don't know her at all," Williams said. "I see her around the locker room a little bit. She's always smiling, so she seems to be super sweet. I know Venus has played her before. I've watched that match a few times. I feel like she does really well on grass. ... So, yeah, I know it's not going to be easy for me. She has nothing to lose. She's going forward."
Maria Sharapova also made her way into the third round, two years after losing at the same stage.
The fourth-seeded Sharapova beat Dutch qualifier Richel Hogenkamp 6-3, 6-1 on Court No. 2 to improve her record in second-round Grand Slam matches to 41-4.
The Russian struggled with her serve -- she had eight double faults -- but she made up for it with 23 winners.
In 2013, Sharapova lost to Michelle Larcher De Brito in the second round. Last year, the Russian lost in the fourth round at Wimbledon.
Sharapova won the first of her five major titles at Wimbledon in 2004. She has been back in the final at the All England Club only once since then, losing to Petra Kvitova in 2011.
In one of the day's biggest surprises, 158th-ranked American qualifier Bethanie Mattek-Sands upset seventh-seeded Ana Ivanovic 6-3, 6-4.
Mattek-Sands, who was out for six months last year with a left hip injury, had 32 winners, more than twice the number for Ivanovic, a former No. 1 player who reached the semifinals in 2007.
Coco Vandeweghe of the United States made it to the third round for the first time, upsetting 11th-seeded Karolina Pliskova of the Czech Republic 7-6 (5), 6-4. Vandeweghe will next face 22nd-seeded Samantha Stosur, the 2011 US Open champion.
Another American, No. 21 Madison Keys, downed Stefanie Voegele of Switzerland 6-7 (6), 6-3, 6-4.
The Associated Press contributed to this report.