Venus Williams will have to lean on her younger sister if she wants to add another Olympic medal.
The U.S. stalwart was upset 4-6, 6-3, 7-6 (5) by Belgium's Kirsten Flipkens on Saturday in the first round of the Rio Games, a disappointing showing for the No. 5 seed in what figures to be her final Olympics.
MORE: Full medal count | Rio Olympics TV schedule
Flipkens collapsed on the green hardcourt in elation after winning the third-set tiebreaker, exhausted after a match that lasted three hours, 13 minutes. The decisive tiebreak came moments after the Belgian was broken at love by Williams when she had a chance to serve out the match.
Williams, 36, won the singles gold medal 16 years ago in Sydney and has doubles gold medals with sister Serena from 2000, 2008 and 2012. The Williams sisters are the top seed in the Rio doubles tournament.
Williams' loss capped a tough day for the U.S. on the courts. Earlier, Sloane Stephens fell 6-3, 6-3 to Canada's Eugenie Bouchard and two U.S. men lost to Japanese opponents: 14th-seeded Jack Sock falling 6-4, 6-4 to Taro Daniel and Brian Baker 5-7, 7-5, 6-4 to Yuichi Sugita.
On the positive side for the Americans, seventh-seeded Madison Keys advanced easily against Danka Kovinic with a 6-3, 6-3 win and 12th-seeded Steve Johnson cruised 6-3, 6-2 against Darian King of Barbados.
