Wang Qiang into 4th round after Serena withdraws, Osaka stunned

China's Wang Qiang advanced into the fourth round of the WTA and ATP Miami Open by walkover on Saturday as Serena Williams unexpectedly pulled out, blaming a previously undisclosed left knee injury.

The 37-year-old American superstar's withdrawal comes a day after Wang, who made the round of 16 at the BNP Paribas Tennis Open earlier this month, comfortably swatted aside Britain's Johanna Konta 6-4, 6-0 to reach the third round.

Williams showed no signs of injury a day earlier while winning her opening match against Rebecca Peterson, 6-3, 1-6, 6-1 and the 23-time Grand Slam champion didn't mention any health issues during a news conference after the match.

Serena Williams in action at the Miami Open in the Hard Rock Stadium in Miami Gardens on March 22, 2019. /VCG Photo

"I am disappointed to withdraw. It was an amazing experience to play at Hard Rock Stadium this year, and I would like to thank the Miami Open for putting on an amazing event," Williams said in a statement.

"I hope to be back next year to play at this one-of-a-kind tournament in front of the incredible fans here in Miami."

Osaka toppled

Less than two hours after Williams' withdrawal, Naomi Osaka also crashed out after Hsieh Su-wei of Chinese Taipei put on another strong performance beating the world number one 4-6, 7-6 (7/4), 6-3.

Hsieh Su-wei makes an impressive start on the main court of the new look Miami Open. /VCG Photo

"This was a very emotional win for me," said Hsieh who hit 39 winners, one less than her opponent, with both winning 69 percent of points on their first serves. "Any time you beat one of the top players, it is amazing."

The 33-year-old Hsieh will play either Caroline Wozniacki or Monica Niculescu in the fourth round, while Osaka's departure matched the earliest ever in the tournament by a top-seeded woman and jeopardized her No. 1 ranking, depending on results next week.

"I feel like I've dealt with the stress of people asking me do I have pressure because I have the No. 1 next to my name," Osaka said. "I thought I was doing fine with that, but I guess I'm not."

Osaka's defeat follows her fourth-round exit last week at Indian Wells, where she was the defending champion. /VCG Photo

Earlier in the day, world number two Petra Kvitova overcame Croatia's Donna Vekic 6-4 3-6 6-4 in a tensely contested three-setter that lasted more than two-and-a-half hours.

Kvitova, the third seed, will meet France's Caroline Garcia, who knocked out 15th seed Julia Goerges of Germany 6-0, 7-5, in the fourth round.

(With input from agencies)