FLUSHING, N.Y. -- Serena Williams kept Victoria Azarenka waiting.As Williams flopped to the ground, sprawled on her back and clutched her hands to her face in stunned celebration, Azarenka leaned across the net at center court, waiting to shake hands with the new U.S. Open champion.Once Williams, a 6-2, 2-6, 7-5 victor, had danced her way to the net to give Azarenka a hug, the vanquished top seed from Belarus slumped in her courtside chair and buried her head in a towel.The championship was Williams' fourth U.S. Open but first since 2008 and comes 13 years after her first title in 1999.Her 15 majors brings her to within nine of all-time singles leader Margaret Smith Court. Chris Evert and Martina Navratilova each hold 18.The win also raises Williams' record in major finals to an astounding 15-4 and enhances her record since last summer to 71-5.At nearly 31 years old, she is the second oldest champion since Court won her fifth title in 1973.Heading into the final, Williams, who had dropped just 19 games in six matches over the past two weeks, seemed to be a sure thing to beat Azarenka, just as she had in nine of their 10 previous meetings, the most recent in the semifinals of the Olympics.The 34-minute first set did nothing to dispel that rumor as Williams roared to a 4-1 lead.But Williams lacked both her usual fire and passion, more often guiding the ball rather than punishing it.While she had 13 aces over the course of the 2-hour, 18-minute final, she also hit five double faults; while she hit 44 winners, she also struck 45 unforced errors.Azarenka, meanwhile, had no aces, four double faults; she hit just 13 winners and committed 28 unforced errors."I definitely had to relax," said Williams, who has now won championships at the U.S. Open in three different decades. "The more relaxed I am the better I play. I got a little bit tense, a little tight, and things weren't looking good."Midway through the third set Williams twice fought back from a break down, including with Azarenka serving for the match at 5-4. (She was actually two points from the match on Williams' serve at 3-5.)But after Williams took a 79-mph first serve and whaled it back for a winner, the American won 13 of the next 17 points.At 5-6, the Belarusian had two chances to force a third-set tiebreaker but Williams bullied her first with a winner behind her back.Azarenka missed the other when her backhand down the line found its way into the net. Two points later, Williams was on the ground."Being so close it hurts deeply to know you don't have it," said Azarenka, who on the strength of her win at the Australian Open in January, as well as three other WTA Tour titles this year, will retain the No. 1 world ranking.Williams, who also won Wimbledon and the Olympic gold medal, holds steady at No. 4."Could it have gone my way? Probably yes, but it didn't," Azarenka said. "These emotions come out and you feel sad. It was a close match but not for me."For Williams, the ups and downs of the past few years -- including a frightening pulmonary embolism at the beginning of 2011, as well as a first-round upset at the French Open in June -- make this victory that much sweeter."I was miserable after that loss in Paris," said the new champion, a runner-up to Samantha Stosur here last year. "Losses really motivate me. Like I want to go home and do better."Wins motivate me as well because I'm a perfectionist," Williams added, eying the silver chalice on the table in front of her. "Right now the motivation is so up there. I feel like I'm ready for the next tournament. I just want to keep the dream alive."