Ash Barty opened her fourth-round match against Alison Riske with four straight aces and finished her 2019 Wimbledon with a first-service percentage of 53 per cent.

The Australian world No.1 was worn down by the American 6-3 2-6 3-6 who said after the upset that she had to be aggressive against Barty.

“I’m so excited. I think I’m just so proud of myself for the way I handled this match … I couldn’t be more proud of myself,” Riske told Channel Seven.

“I had to play aggressive and I had to take it to Ash and I think that is what I did today.”

After her stellar opening game, Barty initially went on to exert her control, breaking the American in the fourth game and almost doing the same in the sixth before unforced errors proved costly.

Alison Riske battles to hold out Ash Barty in the first set. Photo: Getty

Riske pulled out some power shots to break back in the seventh game, but Barty broke back in the eighth and quickly closed out the first set on serve.

In the second set Barty was broken in the fourth game as she struggled with her first service and Riske upped her tempo.

But the Australian had no answers as Riske mixed up her shots and offered deep returns.

In the third set Barty continued to struggle on first serves, but managed to carve out a break point in game four without managing to capitalise.

The world No.1 was eventually worn down by Riske’s aggressive shotmaking, broken in the eighth game and unable to break Riske’s increasingly confident service game.

The upset was masterminded by Australian Craig O’Shannessy – chief strategist for the men’s No.1 Novak Djokovic – who was commissioned by Riske’s coach Billy Heiser to help devise a game plan to stop Barty’s 15-match winning streak.

The 23-year-old Barty offered no excuses after her exit on Court 2, saying Riske deserved to win.

“Tough one,” Barty told Tennis Australia.

“I started really well, was able to hit my spots. In the second set, I gave Alison too many looks at second serves. I know that my percentage was down. I wasn’t missing serves by too much.

“They were small margins. A miss is still a miss, and gives her an opportunity to have a look at a second serve.

“Overall I didn’t play a poor match. When I needed to, when the big moments were there, Alison played better today. Tough one to swallow, but I lost to a better player.”

“Overall I didn’t play a poor match. When I needed to, when the big moments were there, Alison played better today. Tough one to swallow, but I lost to a better player.” – Ash Barty #Wimbledonhttps://t.co/0He6bFePKM

— TennisAustralia (@TennisAustralia) July 8, 2019

Riske progresses to her first ever grand slam quarter-final, where she will play Serena Williams or Carla Suarez Navarro.

“You just have to look at her stats on a grass court to show just how dangerous she is. She’s very comfortable on the grass court. It complements her game well,” Barty said.

“In the crunch moments, she came up with her best tennis.

“When her back is against the wall, she plays really well typically. She did that today. All credit to her.

“She deserves to be in the quarter-finals.”

Barty said she had “absolutely no regrets” after a thorough preparation.

“I didn’t win a tennis match. It’s not the end of the world,” Barty said.

“It’s a game. I love playing the game. I do everything in my power to try and win every single tennis match. But that’s not the case.

“It’s disappointing right now. Give me an hour or so, we’ll be all good. The sun’s still going to come up tomorrow.”

Barty will return to Brisbane for a well-earned rest before beginning her American hardcourt campaign in Montreal from August 5.

“It’s also important to really celebrate what we’ve been able to achieve over the last eight weeks. It’s been an extremely positive time for me and my team,” she said.

“Go and rest and recover with the family back home, then switch focus back to the hard courts.

“In the US, which I love that time of year, I love getting back over to the summertime there.

“I have some really good memories from last year. We go back, we knuckle down, train again, then we go again.”

-with AAP