WUHAN, China -- No.3 seed Angelique Kerber of Germany advanced to the third round of the Dongfeng Motor Wuhan Open on Tuesday, moving past World No.18 Madison Keys of the United States, 6-0, 4-1, retired. Keys retired from the match due to a left knee injury.

"I was feeling good, I played the first set really well," Kerber told the media, after the match ended. "Of course when you are stepping on court, you are not looking to finish the match like that. I hope that Madison is good very soon. I hope she will recover very fast, and maybe she can play then next week."

Reigning Wimbledon champion Kerber played lights-out tennis in the first set, as Keys eventually struggled due to injury, finally calling it quits during the second set after only 53 minutes on court. Kerber picked up her eighth win in ten meetings with Keys, avenging a tough loss in their most recent match in Cincinnati earlier this summer.

Former World No.1 Kerber had 12 winners to Keys' five, while the American was undone by a whopping 22 unforced errors. Kerber faced only two break points, both in her first service game, and saved them both, while breaking Keys five times during the tilt.

"I think you have to find a rhythm, especially at the beginning of a tournament, and, for me, I was playing good from the first point," said Kerber. "I was also practicing good the last two days here."

"Every day is a new day," Kerber continued. "We are at the end of the season, so now it’s actually time to look day by day, and try to stay in the moment. It doesn’t matter against who you play, just looking to play a good match again, and again, until the last one."

In the round of 16, 30-year-old Kerber will take on last year's finalist Ashleigh Barty, the No.16 seed, who overcame home country favorite Zheng Saisai of China, 4-6, 6-1, 6-2. Kerber has won two of her three previous meetings with Barty.

"I think it is always tricky to play against her," Kerber admitted, regarding Barty. "She can play everything, and she also played here very well in the last years, especially last year. I think it will be a good match, and I’m looking forward to again trying to play my best."

Kerber kicked off a pristine set by quickly breaking an error-prone Keys in the first game. The German raced to a 40-0 lead in the following game before three double faults in the next four points, alongside the American’s first winner, brought Keys to an unexpected break point. But Kerber fended it off with a forehand winner down the line, and eventually held for 2-0.

After that escape, the former World No.1 was off to the races, rolling through the remainder of the set while Keys struggled to keep her shots in play. Keys had two game points at 4-0, but squandered them both with long forehand errors, and then double faulted the game away to hand a 5-0 lead to Kerber.

Kerber reached set point by forcing an error with her forehand, and repeated the feat to close out the set one point later. The German claimed 63 percent of points on the Keys serve in the opening frame. On the other hand, Keys had only two winners in the set, which were counteracted by 13 unforced errors.

Keys finally got on the scoreboard in the first game of the second set, but that would be her only digit of the day, as Kerber quickly took command by breaking for a 2-1 lead. At this juncture, Keys took a medical timeout as the trainer tended to her knee.

The pause did not hinder Kerber’s play in the least, as the three-time Grand Slam champion fired multiple forehand winners to hold for 3-1. Keys tried to power her way through the next game with her typically fiery groundstrokes, but it was to no avail, and after Kerber blasted a forehand return off of an iffy second serve to break once more, the American pulled the plug, sending Kerber into round three.

"My knee was bothering me even before today," Keys told the media, following her retirement. "I had it taped yesterday, and when I woke up it didn’t feel any better. I tried to tape it again today, which obviously didn’t work, and when you are playing someone like Angie who is going to make you move, you need to feel like you are moving well. And I just couldn’t do that today.”