KEY BISCAYNE, Fla. (AP) -- Roger Federer let a big lead slip away in the second set, then regrouped to win his opening match Saturday at the Sony Ericsson Open, beating 19-year-old American Ryan Harrison 6-2, 7-6 (3).
Federer led 5-2 in the second set and was on the verge of finishing in less than an hour when he lost two fluky points that extended the match.
Serving at 5-3, Federer blew an easy overhead to fall behind 15-30. Federer then stopped playing when he mistook a shout from the stands for a linesman's call, which cost him the next point, and he went on to lose serve.
The match continued for another 25 minutes before Federer closed it out for his 40th victory in the past 42 matches. He extended to 77 matches his winning streak against players outside the top 20.
Federer's opponent in the third round will be Andy Roddick, who never faced a break point as he beat Gilles Muller 6-3, 6-2. Roddick hopes to improve a ranking that has dropped to 34th, the lowest he has been since 2001.
Roddick is 2-21 against Federer, but did beat him at Key Biscayne in 2008.
"There's no getting around the fact that he has been the biggest obstacle in my career," Roddick said. "His game matches up well against mine."
Serena Williams started early and finished fast. Walking onto the stadium court at 11 a.m., Williams dominated with her serve, played consistently from the baseline and moved into the fourth round by beating Roberta Vinci 6-2, 6-1.
Williams was done shortly after noon.
"I'm not a morning person," she said. "I actually hate morning matches, but I always do my best at 11 o'clock matches."
Williams won most of the short points and a succession of long rallies as well. She hit 25 winners while committing 20 unforced errors.
Seeded 10th, Williams is making her return to tournament tennis after a two-month absence because of a left ankle injury. At No. 20, Vinci is the highest-ranked player Williams has beaten this year.
Williams is seeking her first tournament championship since August, and she's bidding for a record sixth title at Key Biscayne.
"I need trophies," she said. "I want to add more and to do more. There are records to break. So I'll do it. I've just got to believe it. I do believe it."
No. 12-seeded Sabine Lisicki edged No. 17 Peng Shuai 6-4, 7-5.
Seeded men swept the day's first nine matches. Winners included No. 5 David Ferrer, No. 14 Gael Monfils, No. 17 Richard Gasquet and No. 20 Fernando Verdasco.