Angelique Kerber through to US Open semifinals

Both players struggled to hold serve in the first set and Kerber, the world's No.2 women's player, looked in some trouble at 5-4 down with Vinci needing just two points to take the set. However, she wrestled control of the match by winning three straight games to take the opener 7-5. A foot fault from Vinci in the final game helped Kerber's cause and saw the Italian clash with the line judge who made the call.

Once she'd taken the lead, Kerber didn't let up. She extended her run of consecutive games to nine to claim the second set with minimum fuss and exertion 6-0. Her opponent won just 10 points in the entire set. This is the second time (after 2011) that Kerber has made it to the semifinals at Flushing Meadows.

Despite rattling through the second set in just 24 minutes, Kerber said she'd been in a genuine contest.

"It's always hard against Roberta. I am so happy that I won in two sets," she said. "I tried to stay calm when it was tight. That was the key in the first set . It means a lot to me to be standing here again in the semifinals."

Kerber will face Denmark's Caroline Wozniacki in the semifinals on Thursday after she beat surprise quarterfinalist Anastasija Sevastova of Latvia 6-0, 6-2.

The win also keeps her on course for another Grand Slam final against Serena Williams, who Kerber beat in the final of the Australian Open earlier this year and lost to in the Wimbledon final. The pair are also battling it out for the No. 1 spot in the women's ranking.

Kerber said after her quarterfinal win that she wanted to maintain her levels of concentration throughout the tournament as she bids for a second career grand slam tournament win.

"I'm trying to improve, of course, my mental side, because I know I need to stay focused on my game, trying to be here in this moment and not thinking about what's happened and just thinking about the positive things," she said.

"Just going for it and just trying to stay a little bit relaxed when it's close and just go for it when I have the chance."

Djokovic watches another opponent pull out

On the men's side, the world No. 1, Novak Djokovic, had an easy time of it yet again, after the No. 9 player, Jo-Wilfried Tsonga, pulled out due to a knee injury, two sets into their quarterfinal, with the Serbian leading the match 6-3, 6-2.

This came after Djokovic's second-round opponent, Jiri Vesely, and his third-round opponent, Mikhail Youzhny, both quit early due to injuries.

"Of course, this Grand Slam is very unique for me: I never experienced something like this - to have three retirements on the road to the semifinals," said Djokovic, who will face Gael Monfils in the semis, after the No. 12 player beat his French countryman, Lucas Pouille, 6-4, 6-3, 6-3.