Bencic sends Venus crashing out of Australian Open: Stephens tumbles out in first round, Ostapenko impresses

The 20-year-old Swiss played the 37-year-old American great to perfection, soaking up the fifth-seed's firepower and attacking her wavering serve with abandon under the roof at Rod Laver Arena.

In a tense grand slam opener that felt more like a final, Venus battled to keep touch in an enthralling second set but Bencic unleashed two blazing forehand winners to close out the match in the 12th game.

The resurgent Bencic will meet the winner of Johanna Larsson and Luksika Kumkhum in the next round.

In men's competition, Sloane Stephens became the first big casualty at this year's Australian Open as the U.S. Open champion tumbled out in the first round against China's Zhang Shuai.

The American 13th seed, who is without a win since her triumph at Flushing Meadows, looked assured as she took the opening set but Zhang hit back to win 2-6 7-6(2) 6-2 on Margaret Court Arena.

Stephens was not the only new member of the grand slam winners' club in action on Monday, though French Open champion Jelena Ostapenko fared far better with 6-1 6-4 defeat of Italian Francesca Schiavone in the first match on Rod Laver Arena.

Schiavone, who won the French Open in 2010, threatened to take the second set before Latvian Ostapenko, seeded seven, clicked back into gear to ease through.

Stephens was assured in winning the first set but Zhang, who reached the quarter-finals in 2016 as a qualifier, found her rhythm and after taking the second set on a tiebreak dominated the decider with her American opponent wilting in the face of the pinpoint accuracy of the world number 34.

Stephens, who withdrew from the Brisbane warmup event with a right knee injury, reached the semi-finals in Melbourne in 2013 but lost in the first round in 2015 and 2016 and missed out through injury last year.