In her first match at the Australian Open since a Williams sister was guaranteed to win the title, Venus Williams lost in the first round to Belinda Bencic and ensured it cannot happen in 2018.
Venus lost last year's final at Melbourne Park to younger sibling Serena, who clinched an Open era-record 23rd major but hasn't played a Grand Slam tournament since because of her pregnancy and the birth of her first child.
The 6-3, 7-5 loss for Venus Williams was her first in five career meeting with Bencic, who lost to Serena Williams in the first round here last year.
The 20-year-old Bencic saved five break points in the eighth game before a rain delay caused an almost half-hour suspension of play as the roof was closed on Rod Laver Arena. She returned on a roll, winning the next six points to hold serve and then clinch the set.
Bencic teamed up with Roger Federer to win the Hopman Cup for Switzerland in the first week of the season, and had the 19-time major winner's parents in the crowd supporting her on Monday.
It must have helped, having overcome the surprise when the draw was made that she'd have to play another Williams in the first round.
"Honestly, the first reaction of everyone was 'Oh, bad luck.' But of course, it would be nice to play somebody easier first round and get your rhythm a little bit," Bencic said.
"It's amazing, when I was a little girl, I was watching them on TV. I never thought I'd get a chance to play them."
Williams' exit followed U.S. Open champion Sloane Stephens' 2-6, 7-6 (2), 6-2 loss to Zhang Shuai.
No. 13-seeded Stephens was serving for the match in the 10th game of the second set but dropped her serve. She was outplayed in the tiebreaker and in the third set.
It always shaped as a tough opener for Stephens, who hasn't won a tour-level match since her Grand Slam breakthrough triumph at the U.S. Open last year and facing a player ranked No. 34, two spots off being seeded for the first major of the season.
Stephens didn't play last year's Australian Open because of a left foot injury that kept her out of action until Wimbledon. Since beating Madison Keys in the U.S. Open final, Stephens has lost eight matches.
"Sloane she plays so well, won the U.S. Open - everyone knows - she's a great player," Zhang said. "I know how hard I'm working ... coming to Australia I'm ready for every match, every player. That's why I won today."
French Open champion Jelena Ostapenko made a positive start with a 6-1, 6-4 win over 37-year-old Francesca Schiavone, the 2010 French Open winner.
Ostapenko saved two break points in the third game of the opening set and clinched the set with an ace. After an exchange of service breaks in the second, Ostapenko got the decisive break in the ninth game, then served out the match after double-faulting on her first match point.
Three other Americans went out in earlier matches, with 10th-seeded CoCo Vandeweghe losing to Timea Babos 7-6 (4), 6-2, 12th-seeded Julia Goerges extended her winning streak to 15 matches with a 6-4, 6-4 win over Sofia Kenin, and No. 19 Magdalena Rybarikova beating Taylor Townsend 6-0, 7-5.