Australia’s Samantha Stosur has lost to China’s Zhang Shuai in the second round of the US Open on Friday (AEST).

Stosur was on the back foot for much of the match, going down 6-3, 6-3 on the Grandstand court.

Zhang broke Stosur in the fifth, seventh and ninth games of the opening set – balanced by one break back for the Australian – to take a 1-0 lead after 32 minutes.

The Chinese player raised the pressure on Stosur’s serve, and the critical game was the fourth of the second set.

Stosur fought off two break points before Zhang pounced, nailing a deep backhand winner into the corner before a running forehand pass down the line gave her the break for 3-1.

The Australian forced a forehand error from Zhang to bring up break point in the following game, but her opponent hit back, drawing three consecutive errors off the Stosur racquet to take the game for a 4-1 lead.

Shuai Zhang celebrates taking the first set against Samantha Stosur. Photo: Getty

Stosur held, then had another break point on Zhang’s serve, but the world number 51 consolidated her lead to move within a game of taking the match.

The 16th seed held again to 3-5, but the Chinese player’s powerful groundstrokes proved too strong, as she clinched the match after one hour nine minutes.

Stosur converted only one of five break points for the match, and won only 18 points out of 57 on her opponent’s serve.

Her departure from the tournament means the only Australian left in singles’ competition is Nick Kyrgios, who will play Horacio Zeballos of Argentina later on Friday.

Meanwhile, Bernard Tomic has been fined for his foul-mouthed spray at a US Open heckler.

Tomic has been fined $US10,000 ($A13,300) for yelling profanity at a fan during his first-round loss to Bosnian Damir Dzumhur on Tuesday.

Tomic’s camp insist he was severely provoked, but ITF officials deemed the Australian’s expletive-laden rant as unsportsmanlike conduct.