Melbourne: Hobbling former champion Stan Wawrinka was knocked out of the Australian Open by American Tennys Sandgren on Thursday, losing 6-2 6-1 6-4 on the Margaret Court Arena.
The Swiss 32-year-old looked to be struggling with his movement against the world number 97, clutching his knee throughout the match, especially when forced wide.
Sandgren, 26, played rock-solid tennis to claim only his second grand slam singles victory having opened his account against Frenchman Jeremy Chardy in the first round.
He completed victory with an ace.
Wawrinka had right knee surgery in August and Tuesday's victory over Ricardas Berankis was his first match for six months, having only declared himself fit last weekend.