Reigning US Open champion Osaka knocked out by Bencic

Both defending champions and No. 1 seeds, Osaka and Novak Djokovic, are gone before the quarterfinals at the year’s last Grand Slam tournament.

Osaka has been wearing a black sleeve on her bothersome left knee and was visited by a trainer during the second set.   -  GETTY IMAGES/AFP

Naomi Osaka’s 10-match U.S. Open winning streak and title defense are done after she was outplayed in the fourth round by Belinda Bencic and lost 7-5, 6-4.

Osaka has been wearing a black sleeve on her bothersome left knee and was visited by a trainer after getting broken to trail 3-2 in the second set.

The result under the closed roof at Arthur Ashe Stadium on a rainy Monday means both defending champions and No. 1 seeds are gone before the quarterfinals at the year’s last Grand Slam tournament.

Novak Djokovic stopped playing in his fourth-round match against Stan Wawrinka on Sunday night because of a painful left shoulder.

READ : Reigning US Open champion Osaka knocked out by Bencic

Osaka made her breakthrough at Flushing Meadows a year ago, winning her first major championship by beating Serena Williams in a chaotic final that devolved after Williams got into an extended argument with the chair umpire.

Osaka followed that up with a second consecutive Grand Slam trophy at the Australian Open in January. That allowed her to become the first tennis player representing Japan to reach No. 1 in the rankings.

The 13th-seeded Bencic, who is from Switzerland and has been mentored by Martina Hingis, showed again that she is a big-match player. She improved to 3-0 against Osaka this season and now has a tour-leading nine victories over top-10 opponents in 2019.

“The challenge cannot be bigger against Naomi. I had to be at the top of my game and I'm really pleased how well I handled my nerves at the end,” said Bencic, who also beat Osaka at Indian Wells and Madrid.

“I'm trying to play like chess and make it tactical on the court,” she added. “Taking the serve early, trying to anticipate because she has so much power.”

Bencic also is 4-1 over her career against top-ranked players.

READ : Djokovic losing ground on Federer and Nadal will sting more than shoulder pain

Mertens reaches quarters

Belgian 25th seed Elise Mertens cruised into her first US Open quarterfinals by dispatching 141st-ranked US wildcard Kristie Ahn 6-1, 6-1.

Mertens needed a mere 67 minutes dismiss the 141st-ranked Ahn, a 27-year-old American who had become the comeback story of the tournament with an 11-year gap between Flushing Meadows appearances.

Mertens hit 17 winners and took advantage of 25 unforced errors from her opponent.

For Mertens, it's her second-best showing in a Grand Slam event, after reaching the semis of the Australian Open last year.

She moves on to play the winner of the match between American qualifier Taylor Townsend and 15th-seeded Bianca Andreescu.

Andreescu beats Townsend

Canadian teenager Bianca Andreescu, seeded no. 15, has defeated 116th-ranked Taylor Townsend of the United States 6-1, 4-6, 6-2 to advance to the quarterfinals of the US Open.

Andreescu, 19, who clinched her second professional title at the Women’s Tennis Association Premier 5 event in Toronto, needed just one hour and 55 minutes to reach her first Grand Slam quarterfinals, reports Efe news.

The Canadian teen ended the game, held in the Arthur Ashe Stadium at Flushing Meadows, with 33 winners and 26 unforced errors but committed eight double faults, which cost her the second set.

Meanwhile, 23-year-old Townsend won only 16 of 40 net points and struck 25 winners while committing 24 unforced errors.

However, the American’s serve was no match for Andreescu’s returns from the baseline and she was always at the mercy of the rhythm set by the Canadian player, who won 50 percent (41 of 82) of her receiving points against Townsend’s serve.

Andreescu will now meet 23rd-seeded Belgian Elise Mertens, who easily defeated American Kristie Ahn, world No. 141, to qualify for her first US Open quarterfinal in four appearances.