'Completely done': Truth emerges about Ash Barty's US Open loss

Ash Barty's coach has revealed the tactical blunder he made in the lead-up the World No.1's shock loss in the third round at the US Open.

Barty suffered a stunning loss to American Shelby Rogers in New York, bowing out after blowing a 5-2 lead in the third set.

REVEALED: New photo shows truth about Serena and Sharapova

'RIDICULOUS': Coach's bombshell revelation about Ash Barty

Tennis fans were left scratching their heads after the World No.1's shock exit, and coach Craig Tyzzer has now gone some way to explaining what went wrong.

With Barty and Tyzzer both finding the conditions at Flushing Meadows vastly different to where the Australian won her fifth title of the season in Cincinnati, Tyzzer opted to change the top seed's racquet strings before her match against Rogers.

"Look, it was super different conditions," Tyzzer told AAP.

"The men use a different ball to the women at the US Open and the women's ball is really light and it gets faster.

"All the stats show that most of the girls, when the ball got older, their actual shots got faster.

"It was super tough to control the ball and to keep it in the court and I actually, for her third-round match, took the gut out of her racquet because she was struggling in the first two rounds to keep the ball in court.

"I mean, she did a great job getting through. She literally could not get the ball up and down with any sort of spin.

"So we put full poly in her racquet for her third-round match in the hope that she could just get a little bit more feel.

"It took a bit of weight off her serve, which is not ideal for her, just to give her that confidence in being able to hit off the ground and play."

Coach says tactical blunder didn't cause Ash Barty's loss

With Barty making a raft of unforced errors in dropping the opening set 6-2, the tinker may have affected the title favourite's rhythm.

But while he took full responsibility, Tyzzer said neither he or Barty blamed the change for her defeat.

"The conditions suited players who are counter-punchers and stay up on the baseline and hit flat because the courts are dead but the ball is pretty lively and flies through the court," Tyzzer said from quarantine in Melbourne.

"But in the end, it wasn't down to that. She was just physically and mentally exhausted; completely done.

"She just didn't have anything left in the tank, unfortunately."

Asked if Barty was cranky with him, Tyzzer said: "Look, she probably could be but it was more that I just wanted to ease her mind about having feel and playing with the conditions.

"It wasn't her decision - it was my decision.

"In the end, I don't think it cost her the match because she'd basically gone 6-1 5-1 (in the second and third sets) playing the right way and just ran out of steam.

"I think the decision was right with the string because she was able to do more of the things that she wanted to do other than probably serve better."

with AAP

Click here to sign up to our newsletter for all the latest and breaking stories from Australia and around the world.