KEY BISCAYNE, Fla. (AP) -- Trailing in the first set of her first match at the Sony Open, Serena Williams grunted with every shot and screamed with every point she won.
And then, on the pivotal point, she didn't make a sound - or take a swing.
Williams capitalized on a critical double-fault Thursday by Yaroslava Shvedova to survive a 69-minute first set and win, 7-6 (7), 6-2.
''It was an incredibly tough first set,'' Williams said. ''I just needed to relax and yet keep up the intensity.''
The top-ranked Williams seeks a record seventh Key Biscayne title, and her second in a row.
No. 4-seeded Maria Sharapova, a five-time runner-up in the tournament, joined Williams in the third round by beating Kurumi Nara 6-3, 6-4. Seeded players had first-round byes.
On the men's side, Lleyton Hewitt became the third active man to win 600 matches when he rallied past Robin Haase 3-6, 6-3, 6-3.
Fellow Australian Bernard Tomic lasted only 28 minutes in the shortest match since the ATP started keeping such records in 1991. Tomic, mounting a comeback from surgery on both hips and playing for the first time since January, won just 13 points and lost to Jarkko Nieminen 6-0, 6-1.
''I did the best as I could,'' Tomic said. ''Hopefully in a little bit of time I can get back to 100 percent.''
Americans Jack Sock, Ryan Harrison, Sam Querrey and Donald Young won first-round matches.
Williams, who owns a small share of the Miami Dolphins, wore a dress in the team's orange and turquoise colors - which may explain her slow start. Or maybe it was because she hadn't played since Feb. 21.
Williams had to erase a 5-3 deficit in the first set, and then fell behind 6-3 in the tiebreaker. Shvedova pushed a forehand into the net, then hit a nervous double-fault that allowed Williams to exhale.
She won the next two points with aces, and then closed out the set with a backhand winner, a fist pump and a scream of ''Yes!''
Her game steadied in the second set, when she had 18 winners and only 10 unforced errors - bad news perhaps for opponents to come in the tournament Williams considers her hometown event. She lives an hour up I-95 in Palm Beach Gardens.
''I obviously love playing here,'' she told the crowd. ''I'm just happy to have a win today.''
The 33-year-old Hewitt also staged a comeback. With the victory, he joined Roger Federer (942 wins) and Rafael Nadal (675) in reaching the 600 milestone.
''Not many people get the opportunity to get close to that, so it means I have been around for an awfully long time,'' Hewitt said. ''I'm getting old. A few years ago when I had the last couple of surgeries, I probably would have doubted I'd get to this stage. I'm grateful I'm out there and able to compete with the best guys.''
Hewitt is a former No. 1 and a three-time Key Biscayne semifinalist.
In other women's play, No. 5-seeded Angelique Kerber won her opening match, beating Peng Shuai 6-3, 1-6, 7-6 (5). Kerber, a two-time Grand Slam semifinalist, matched her best showing at Key Biscayne by reaching the third round.
No. 12 Ana Ivanovic beat American Lauren Davis 6-1, 6-1, and No. 8 Petra Kvitova defeated Paula Ormaechea 6-3, 6-4. No. 28 Svetlana Kuznetsova, the 2006 champion, lost to qualifier Donna Vekic 7-6 (5), 7-5.
Friday's stadium court schedule features the winners of 34 Grand Slam titles in five matches. The parade of champions will include Federer, Novak Djokovic, Venus Williams, Andy Murray and Li Na playing their opening matches.