NEW YORK -- Serena Williams was cruising along in the U.S. Open semifinals, serving up another bagel, when, out of nowhere, a competitive tennis match broke out.
Didn't last long.
The defending champion won the first seven games of Friday's match, then actually fell down a break early in the second set, before quickly regaining it on the way to a 6-0, 6-3 victory over fifth-seeded Li Na.
The day's only drama came in the second-to-last game -- an affair that went eight deuces and lasted 13 minutes, 49 seconds. Li saved six match points, but it only delayed the inevitable. Williams dropped two points in the next game, but ended it and let out a long, celebratory scream after a 107 mph service winner.
"It got tough at the end. I got a little nervous, but I was able to close it out finally," Williams said.
The victory set up a rematch of last year's final against Victoria Azarenka, who beat 83rd-ranked Flavia Pennetta 6-4, 6-2 in the earlier semifinal.
The first set of the Williams match marked the third straight set the No. 1 seed won at love, and when she held serve to open the second, she had won her 24th straight game of the tournament, dating to her match last Sunday against Sloane Stephens.
Nothing lasts forever, of course, though Williams is extending her string of dominance in the women's game deep into a second decade.
Sunday's match will mark her 21st Grand Slam final. She stands one win away from capturing her fifth U.S. Open title and 17th major trophy. This will be the first time the same two women have met in back-to-back finals at Flushing Meadows since it was Williams against her sister, Venus, in 2001-02.
Williams wore pink shoes embroidered with tiny hearts on the heels, each of them with a number inside of it -- `99, `02, `08, `12 -- marking each year she hoisted the trophy in Queens.
She's showing every sign of needing a redesign, and Azarenka is the only one standing in the way.
"We always have really good matches. I look forward to it," Williams said. ` It's great to get to another final. She's a great player and she lifts her game when it really counts."
Azarenka, the 2012 and 2013 Australian Open champion, is trying to become the first woman to win the majors in Melbourne and New York in the same year since Martina Hingis in 1997.