Venus Williams, Sloane Stephens Stunned in Round 1 of 2018 Australian Open

The 2018 Australian Open main draw just began Monday in Melbourne, and two marquee stars are already out of the tournament.

Belinda Bencic upset fifth-seeded Venus Williams 6-3, 7-5, while 13th-seeded Sloane Stephens lost in three sets to Zhang Shuai, 6-2, 6-7 (2), 2-6.

Stephens' 2017 U.S. Open victory was supposed to be a breakthrough. Instead, the 24-year-old is now winless in her last eight singles matches since beating Madison Keys in the U.S. Open final last September.

The margins between Stephens and Zhang were pretty thin. Stephens had 33 winners to Zhang's 28, while the latter won four more points over the course of the entire match.

Unforced errors was one area in which Zhang had a clear advantage. According to the Australian Open's official website, Stephens had 29 unforced errors, while Zhang finished with just 17. Zhang's more measured approach helped her seal the upset.

Williams, meanwhile, had no answer for Bencic's serve. The 20-year-old Swiss won 76 percent of her first-service points and 48 percent of her second-service points. Bencic allowed three more break-point opportunities (11) than Williams but used her strong serve to keep herself alive when she needed to.

Bencic's shocked reaction immediately after securing the victory, courtesy of the Australian Open's Twitter account, was likely mirrored—for different reasons—by American fans watching the match at home:

Jose Morgado of Portuguese newspaper Record thought the draw dealt Williams a rough hand right out of the gate:

Monday represented a dreadful day for American women as a whole. In addition to Williams and Stephens, 10th-seeded CoCo Vandeweghe, Taylor Townsend, Sofia Kenin and Alison Riske lost as well.

Fans in the United States will hope the Australian Open isn't a sign of things to come over the rest of 2018.