World No 1 faces a similar semifinal opponent to the one she tripped up against last year.

A year after one of the most significant and stunning losses of Serena Williams' illustrious career, she has made it back to the same stage of the same tournament: the US Open semifinals.

The stakes and opponent are different. Once again, there is history in the offing.

At Arthur Ashe Stadium in 2015, two wins shy of completing the first calendar-year Grand Slam in more than quarter of a century, Williams was upset in three sets by unseeded Roberta Vinci of Italy.

At Ashe today, two wins shy of claiming a record 23rd major singles title and earning a record 187th consecutive week at No 1 in the WTA rankings, Williams faces 10th-seeded Karolina Pliskova of the Czech Republic. Vinci had never participated in a grand slam singles semifinal. Neither has Pliskova, who hadn't even been past the third round at a major until now.


The 24-year-old Pliskova grew up watching the Williams sisters on TV and she has already eliminated one in this tournament, beating Venus in a third-set tiebreaker after saving a match point in the fourth round.

Pliskova will be trying to become only the fourth woman to beat both Williams sisters at the same major, joining Martina Hingis at the 2001 Australian Open, Justine Henin at the 2007 US Open, and Kim Clijsters at the 2009 US Open. But Pliskova, who leads the tour in aces this season, realises a daunting task awaits her against Williams.

"She's a big hitter and she can have 50 winners and you cannot do much about it," said Pliskova, whose twin sister is also a tennis player. "But I'm still going to hope that there is going to be some chance in the match where I can get my chance and be the one who is playing aggressive."

The other women's semifinal today is No 2 Angelique Kerber of Germany against the 74th-ranked Caroline Wozniacki of Denmark, a former No 1 who is a two-time runner-up at Flushing Meadows.

Swiss third seed Stan Wawrinka outlasted tiring former champion Juan Martin del Potro in four sets yesterday to advance to the men's semifinals.

Two-time grand slam winner Wawrinka ended the rousing comeback effort of the Argentine at Flushing Meadows with a 7-6 (7-5) 4-6 6-3 6-2 win to close out day 10 at the year's last grand slam.

Del Potro, the 2009 winner, had missed nine successive slams due to a string of wrist surgeries before returning to Wimbledon, where he ousted Wawrinka in the second round and went on to claim silver at the Rio Olympics.

"It was an amazing match for me, one of my toughest matches, mentally and physically against Juan Martin," Wawrinka said. "He's an incredible player and I'm really happy to have won that match."

The Argentine had his right shoulder manipulated during a second-set changeover at 2-3 and he responded with a service break for a 4-3 lead and served out the set.

As the match wore on, it became evident that a lack of conditioning was wearing down del Potro and he became selective about which points to contest.

The fit Wawrinka charged to victory, finding the range with his stylish one-handed backhand for winners up the line.

As del Potro went out for the last game, the fans that had remained as the clock moved past 1am serenaded him and the big Argentine wiped away tears as "Ole, ole, ole, ole, Delpo, Delpo," rained down from the Arthur Ashe Stadium stands.

"Something difficult to describe with words," del Potro, ranked 142 and given a wild card into the event, said of the salute. "I can lose the match but I will never forget this. It's bigger than a win in any match."