Venus Williams out after first-round upset by Belgium's Kirsten Flipkens

— -- When Venus Williams pushed one last forehand long to lose in the first round for the first time in her record five Olympic singles tournaments, her opponent celebrated as if having claimed a gold medal, dropping down on the green hard court to plant a kiss on the white five-ring logo.

This was clearly a very big deal to Kirsten Flipkens, a Belgian ranked 62nd and only once as far as the semifinals at a Grand Slam event.

Just two points away from winning on four occasions while portions of the crowd turned hostile toward her, the 36-year-old Williams faded as Saturday night's match stretched past 3 hours and she was stunned 4-6, 6-3, 7-6 (5) by Flipkens on Day 1 of tennis at the Rio de Janeiro Olympics.

The 36-year-old American -- owner of four gold medals and seven Grand Slam titles -- labored at times and showed frustration by shouting "Ridiculous!" after one point Saturday.

Afterward, Williams did not speak to reporters. Instead, U.S. women's tennis coach Mary Joe Fernandez did, saying that Williams was sick before arriving in Brazil. Fernandez added that Williams had cramping, dehydration and an upset stomach after her loss, but still hoped to play doubles Sunday with younger sister Serena.

"I would be highly surprised if she didn't play, because this has been her goal for the last four years -- to come back to the Olympics,'' Fernandez said. "She wants to win a medal so badly in anything. Knowing Venus, she will be out there, no matter how badly she's feeling.''

Williams owns four gold medals: one in singles and three in doubles. She owns 21 Grand Slam titles: seven in singles, 14 in doubles. But she labored at times Saturday and even showed frustration by shouting "Ridiculous!'' after dropping one point.

With U.S. Secretary of State John Kerry watching, the fifth-seeded Williams was broken while serving for the victory at 5-3. She was two points from a win four times but could not close out Flipkens, who is ranked 62nd and reached the semifinals of a major tournament only once.

Williams was coming off a run to the semifinals at Wimbledon last month, her best showing at a major since 2010. That also made her the oldest woman since 1994 to reach a Grand Slam tournament's final four. And it helped her attain her best ranking since revealing in 2011 that she had been diagnosed with Sjongren's syndrome, which can cause joint pain and fatigue.

"She's used to not feeling 100 percent with her Sjongren's, and I think that's why we saw her compete and fight to the end,'' Fernandez said.  "Credit to Flipkens, who hung around and defended so well and made her play extra shots.''

Williams is the first tennis player to participate in singles at five Olympics, and never had failed to reach at least the third round before, claiming a gold at the 2000 Sydney Games. She also won doubles golds in 2000, 2008 and 2012. But against Flipkens, who was making her Olympic debut, Williams failed to find the right measure on most of her strokes and wound up with 13 fewer winners on courts that competitors agree are playing slowly. Williams, once possessor of one of the best serves in women's tennis, hit one ace, five fewer than Flipkens.

"This is just one of the most epic matches in my life,'' Flipkens said.

The fans couldn't seem to settle on which woman they wanted to win. They greeted Williams far more loudly and warmly during prematch introductions, although perhaps that was because of her far-greater name recognition. Later, though, they roared when Williams made mistakes. They clapped when she double-faulted. They even gave her grief for the common and innocuous practice of catching a ball toss that wasn't good.

When one group of spectators bellowed a "USA! USA!'' chant late in the third set, others responded by booing (Kerry had left by then).

"They just enjoyed my game because, I think, I'm a little girl trying to do some special stuff to get a chance to beat a champion like that,'' Flipkens said.