Wang Qiang celebrates a point in her match at the US Open tennis tournament against Ashleigh Barty on Sunday. Photo: IC

Wang Qiang said the memory of her former coach Peter McNamara, the late Australian Davis Cup tennis star and Wimbledon doubles champion, was helping drive her breakthrough run at the US Open. 

The Chinese 18th seed is enjoying her best Grand Slam showing in New York and qualified for the quarterfinals Sunday after a 6-2, 6-4 defeat of reigning French Open champion Ashleigh Barty, the second seed in New York.

"I think I'm really focused on the court, really enjoyed the way I played. I'm so happy I won," Wang said after becoming the first woman from ­China to reach the last eight at the US Open since Peng Shuai made it to the semifinals in 2014.

"Think I did really well today. I'm really mentally strong today. Just keep going."

However, it has proved a challenging year for Wang, 27, following the death of the McNamara in July.

McNamara, a popular figure on the men's and women's tours, passed away at the age of 64 after a battle with prostate cancer.

"He helped me a lot. It was really tough to me to hear he passed," Wang said. 

"I think he has always been there with me."

Wang had worked with McNamara since 2015 until the start of this year, when the Australian's deteriorating health made it harder to travel, ending a partnership that coincided with her cracking the top 20 last season.

"He told me how to play the match. He took me to the professional tennis. So that's how he taught me," Wang said.

"He always believed in me. He told me I can be the top player."

Wang will face Serena Williams, who is seeking a 24th career Grand Slam title to match Margaret Court's all-time record, for a spot in the last four.

Williams, a six-time US Open winner, romped to a 6-3, 6-4 victory over Croatian 22nd seed Petra Martic.

The 37-year-old American star required a medical timeout in the second set after rolling her right ankle as she approached the net but promptly recovered to reach the last eight in New York for the 16th time.

"I feel fine right now physically," said Williams, who received further strapping to an already heavily taped ankle. "But I'll see tomorrow. So far I'm good. I have been managing it. We'll see tomorrow.

Eighth-seeded Williams, who has also suffered knee and back injuries this season, felt a mental setback when it happened but battled through to win.

"I've had a rough year with injuries," she said. "It was like, 'Oh my God. Not again. I'm finally walking.'"

Williams last won a major at the 2017 Australian Open and hasn't won the US Open since 2014.