Zheng Qinwen admitted it was not her day as she was beaten in the Australian Open second round in the biggest shock of the tournament so far.

China's Zheng, runner-up to Aryna Sabalenka last year and the Olympic singles gold medallist, lost 7-6 (7-3) 6-3 to German veteran Laura Siegemund.

The fifth seed is the highest ranked player from either singles draw to lose so far at Melbourne Park.

Zheng was irked by two time violations during the match, one of which cost her a first serve.

She complained to the umpire that she could not see the shot clock, which tells players how long they have left to serve before the 25 second allowance runs out.

"Maybe today is not my day," Zheng, 22, said.

"There's a lot of details in the important points. I didn't do the right choice."