US Open champion Stephens a first-round casualty in Melbourne

American 13th seed and US Open titleholder Sloane Stephens, 24, was upset 2-6, 7-6 (7-2), 6-2 by Zhang Shuai on Monday.

Sloane Stephens and her alarming form slump continued at Melbourne Park.

Sloane Stephens and her alarming form slump continued at Melbourne Park after the US Open champion was bundled out of the Australian Open in the opening round.

Stephens claimed a maiden grand slam at Flushing Meadows last September but the struggling 24-year-old American is still searching for her first win since that triumphant display following Monday's shock three-set loss to Zhang Shuai.

READ: Stephens stuns Keys in improbable U.S. Open final

The 13th seed was up a set and serving for the match at 5-4 in the second on day one of the tournament before Chinese opponent Zhang rallied and completed a stunning 2-6, 7-6 (7-2), 6-2 victory on Margaret Court Arena.

Zhang – who contemplated retirement in 2015 before breaking through for her first slam win at the 2016 Australian Open after 14 attempts – broke twice in the final set as she closed out the first-round upset in just under two hours.