Jennifer Brady has beaten former champion Angelique Kerber in the fourth round of the US Open. Credit: AP
Jennifer Brady has brushed aside former US Open champion and world No.1 Angelique Kerber to reach the quarter-finals of a grand slam for the first time.

The 25-year-old American enjoyed a fine start to the year and has kept that going following the resumption of the tour, winning her first WTA title in Lexington last month.

She went into the tournament as a dark horse and has fully justified that, winning all her matches in straight sets, the latest a 6-1 6-4 victory over 2016 winner Kerber.

And Brady has been joined in the quarter-finals by compatriot Shelby Rogers.

Rogers, the world No.93 stunned Czech sixth seed Petra Kvitova 7-6 (7-5) 3-6 7-6 (8-6) in the US Open fourth round.

Brady bullied her German opponent Kerber from the back of the court during a 22-minute first set.

The second was closer, and there was concern for Brady when she went off-court after five games and returned with her left thigh strapped.

The 28th seed needed more treatment at the changes of ends but she held things together mentally and physically to march across the finish line.

Brady said: "Wow, it feels great, I'm so happy.

"I played a spectacular first set. The second set I really just tried to focus on every single point. I was getting a little frustrated, I felt a little pain in my leg, but I just really wanted to close it out in two sets."

Brady will now face Kazakhstan's Yulia Putintseva in the quarter-finals after a 6-3 2-6 6-4 victory over eighth seeded Croatian Petra Martic.

Kvitova fired a whopping 58 winners and broke serve four times compared to Rogers' two but still walked off court as the loser after two hours and 40 minutes of play.

The 27-year-old Rogers saved four match points during the clash to improve her head-to-head record against Kvitova to 2-0.

Rogers, who defeated Serena Williams in Lexington last month, is into her first US Open quarter-final.

She will play Japanese fourth seed Naomi Osaka who produced a serving master class in a dominating 6-3 6-4 win over 14th seed Anett Kontaveit.

Osaka, the 2018 champion, posted her second victory in 10 days over Kontaveit to reach her first grand slam quarter-final since her 2019 Australian Open title triumph 20 months ago.

Osaka dropped just nine points on serve throughout the entire match, faced zero break points and landed 71 per cent of her first serves in.