Peng Shuai raced into her first grand slam semi-final with a convincing win over 17-year-old Belinda Bencic at the US Open.

The Swiss teenager has attracted most of the attention for her run to the last eight, which included the first two victories over top-10 players of her career.

But she was totally outplayed by Peng, who is yet to drop a set in the tournament and blasted 24 winners in a 6-2 6-1 victory.

The 28-year-old becomes the third Chinese player after two-time grand slam champion Li Na and Zheng Jie to reach the last four at a slam.

The breakthrough has come in her 37th slam tournament, and an emotional Peng said: "It's an amazing time for me. It's a little bit too exciting.

"I love tennis but it's a long time my career, it's been tough sometimes. I was thinking about giving up because I don't know if I can make it.

"I want to say thanks to my coach and my parents because they tell me to fight and never give up. And that today was coming."

Peng showed in the second round by beating Agnieszka Radwanska that she was in great form and she was always in control against Bencic.

The Chinese player, ranked 39th, was simply too consistently good, and it was not long before the teenager was showing her frustration.

Bencic received a warning for coaching by her father Ivan early in the second set and only just avoided a love set.

It has nevertheless been a superb tournament for the teenager, who has worked with Martina Hingis' mother, Melanie Molitor, since she was four and often practises with Hingis.

Ranked 331 a year ago, she is the youngest player in the top 100 and is projected to climb into the top 35 when the rankings are updated next week.

Serena and Venus Williams lost in the quarter-finals of the women's doubles 7-6 (7/5) 6-4 to fourth-seeded Russian pair Ekaterina Makarova and Elena Vesnina.

There was concern for Serena, who plays Flavia Pennetta in the singles quarter-finals on Wednesday, when she took a medical time-out to have her right ankle taped.

The world number one was not at her best throughout and ended the match with consecutive double faults.

Meanwhile, 15-year-old Cici Bellis, who won American hearts by beating Dominika Cibulkova on her US Open debut, lost in the second round of the juniors to Russian Natalia Vikhlyantseva.