Last year's runner-up Venus Williams fell at the first hurdle in the Australian Open when she was knocked out by Belinda Bencic.

Twelve months after Venus was beaten by her sister Serena in the final, the family will not be represented in the second round of the tournament for the first time since 1997.

It was a nightmare draw for fifth seed Williams, with Bencic a former top-10 player herself and back in great form after two years of injury problems.

The 20-year-old finished last season on a 15-match winning streak to book her place at Melbourne Park and won three of her four singles matches against high-class opposition at the Hopman Cup earlier this month.

Williams found herself under pressure from the start and a tally of 32 winners and only 12 unforced errors told how well Bencic played in her 6-3 7-5 victory.

After the final winner, a forehand down the line, Bencic dropped her racket to the court and held her hands to her head in disbelief.

The result will come as a major disappointment to Williams, who was superb at the grand slams last season, making two finals as well as the semi-finals of the US Open.

It compounded an already bad day for the American women, with US Open champion Sloane Stephens continuing her losing run.

Stephens has not won a match since her stunning triumph in New York and a 2-6 7-6 (7/4) 6-2 defeat by Zhang Shuai made it eight defeats in a row.

All four women in the semi-finals at Flushing Meadows were from the US but three of them are already out, with 10th seed Coco Vandeweghe beaten 7-6 (7/4) 6-2 by Hungary's Timea Babos.