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.

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.