FLUSHING MEADOWS, Sept. 4 (Xinhua) -- World No. 1 Victoria Azarenka advanced to the U.S. Open semifinals for the first time on Tuesday with a 6-1, 4-6, 7-6 (5) victory over seventh-seeded defending champion Samantha Stosur of Australia.
The 23-year-old top seed from Belarus ensured that she will remain atop the world rankings no matter what happens the rest of the way in the year's final Grand Slam tournament.
Reigning Australian Open champion Azarenka advanced to a semifinal against either French 11th seed Marion Bartoli or Russian third seed Maria Sharapova, who completed a career Grand Slam by winning this year's French Open.
The match between Bartoli and Sharapova was postponed to Wednesday for the rain disruptions when Bartoli led 4-0 against the Russian.
In the final set tiebreaker, Azarenka raced to a 4-0 lead after Stosur sent a forehand beyond the baseline but the Aussie battled back to level at 5-5 on an overhead smash winner and thanks to a double fault from Azarenka.
Azarenka seized a 6-5 lead on a drop volley after Stosur's shot struck the net cord and plopped over and won the match when the Aussie sent a backhand wide after two hours and 23 minutes.
"I enjoy the fight," Azarenka said. "I enjoy that struggle, that pain that we go through, that incredible moment that you feel relieved after you gave it all in every point you had. I don't want to stop yet."
Azarenka broke Stosur in the first and third games of the opening set before showers struck Arthur Ashe Stadium and halted the match after 10 minutes to win the first set 6-1, which is the first set Stosur lost in US Open.
Stosur, seeking her first title since lifting the trophy last year on the same court, broke to open the second set.
Azarenka broke back in the next game but Stosur broke again to 4-3 with a forehand down-the-line winner and held twice to force a third set. It was the first set Azarenka had dropped in the tournament.
Stosur surrendered a break in the fourth game of the third set by netting a backhand, broke back in the next game on a forehand service return winner, then handed back the break by sending a backhand long to give Azarenka a 4-2 edge.
But Stosur answered again, firing back-to-back forehand winners to break back as both then held serve into the tiebreaker while the tension mounted.
It was the first US Open women's match in the last-eight or deeper to go to a third-set tie-breaker since 2007.
But no women's top seed has won a Grand Slam title since Serena Williams at Wimbledon in 2010 and no US Open women's top seed has taken the title since Justine Henin in 2007.