Switzerland's Stanislas Wawrinka reacts during their men's singles second round match against Tennys Sandgren of the US on day four of the Australian Open tennis tournament in Melbourne on January 18, 2018. Pic/AFP

Struggling Swiss former winner Stan Wawrinka was knocked out of the Australian Open by American Tennys Sandgren in the second round yesterday. The 97th-ranked Sandgren defeated ninth seeded Wawrinka 6-2, 6-1, 6-4 and will next play Germany's Maximilian Marterer. It has been tough so far this year for Wawrinka, who was playing in his first tournament since Wimbledon six months ago following knee surgery.