KEY BISCAYNE, Fla. -- The celebration began with a series of happy hops that propelled Serena Williams across the court. Soon she was twirling, waving, laughing and mugging for the cameras -- a familiar ritual by a perennial champion.
Williams won a record seventh Key Biscayne title Saturday when she overcame a slow start and a set point to beat Li Na 7-5, 6-1 at the Sony Open.
Williams surpassed the tournament record of six titles she shared with Andre Agassi. But on a muggy spring afternoon, the No. 1-ranked Williams looked sluggish at the outset and served poorly, and she was broken twice to fall behind 5-2.
''At that moment I felt like I had nothing to lose,'' Williams said. ''I just was able to relax. Whenever I relax, I enjoy myself.''
Li held a set point serving at 5-4, but Williams erased it with a backhand winner.
Williams needed another 21 minutes to pull out the set. The final game of the set went to deuce six times, but she finally won it with a booming backhand that Li couldn't handle.
Williams ran to her chair with a satisfied scream, her left fist leading the way. She dominated from there, sweeping the final five games, and closed out the victory with a service winner.
The 17-time Grand Slam champion has more titles at Key Biscayne than at any other tournament. She's the fourth woman in the Open era to win an event at least seven times.
''I think we're going to have to rename this tournament,'' former top-five player Mary Joe Fernandez said during the trophy ceremony.
Both finalists are 32, and they shared lots of smiles during the trophy ceremony. Li explained: ''We were talking about, 'For sure before the match they say, 'Oh, two old women.'"
They're close in age, but it's a commentary on the yawning gap between Williams and the rest of the women's tour that she won in straight sets against the No. 2-ranked player while playing less than her best. She made only 44 percent of her first serves and converted just five of 17 break-point chances.
Even so, Williams extended her winning streak against top-10 opponents to 15 matches. She beat Li for the 10th time in a row since 2009.
The world's top-ranked players will also meet in the men's final Sunday, when No. 1 Rafael Nadal tries for his first Key Biscayne title against No. 2 Novak Djokovic, a three-time champion.
Williams lives 90 minutes up I-95 from Key Biscayne and considers it her home event. She said the fans provided a boost when she fell behind.
''It was like, 'Oh my gosh, if I can just hang in here and just try to enjoy myself,''' she said. ''Honestly the crowd pulled me through. I heard some fans go, 'Go Serena!'''
Williams has played in the tournament 14 times and also won the title in 2002-04, 2007-08 and 2013. Her earlier finals victories came against Maria Sharapova, Jelena Jankovic, Justine Henin, Elena Dementieva and Jennifer Capriati twice.
She also lost finals to her sister Venus in 1999 and to Victoria Azarenka in 2009.
Li, who won the Australian Open in January, was at the top of her game for most of the first set. Even so, she couldn't close it out.
''Only one mistake: I think I should go party last night,'' Li said with a smile.
Williams committed six unforced errors in the opening game, and it took her 16 minutes to win a game. She double-faulted to fall behind 5-2, and the comeback came slowly from there.
The first set lasted 73 minutes, longer than many of Williams' matches.