Both Aussies blow up at umpire as bizarre incident causes stoppage in play at US Open

Both Aussie players were left fuming at the chair umpire during a bizarre incident in Tuesday's US Open fourth-round clash.

Alex de Minaur and Jordan Thompson were on serve in the third and one set apiece as they couldn't be separated midway through their round of 16 match.

De Minaur held his service game to love but it was halted momentarily as both players quizzed the umpire.

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De Minaur had hit a lob over the advancing Thompson, sending him scurrying backwards before reaching the ball and scrambling it back in play.

But as he completed the shot his hat fell off his head and onto the court.

He stopped and pointed to his hat, motioning to the umpire and calling out.

But play was allowed to continue as De Minaur returned the ball, much to the bemusement of Thompson.

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The chair umpire finally called hindrance and a let – meaning the point would be replayed – although neither player was particularly impressed.

Thompson furiously walked towards the umpire, as did his Aussie rival, as they asked for clarification.

She explained she was looking up watching the ball, and didn't see the hat.

"I don't think Thompson did that deliberately," Leif Shiras said in commentary.

"It's the brightest piece of clothing he has on … easy to see on the court."

Thompson's hat is fluorescent yellow.