After Sam Kendricks tested positive for COVID-19, Australia announced it had put its entire 54-person track and field team in isolation and subjected it to testing after three athletes reported having casual contact with Kendricks. Charlie Riedel/Associated Press

TOKYO — The fragile nature of an Olympics during the pandemic came into sharp focus Thursday when the entire Australian track team spent time in a brief quarantine after American pole vaulter Sam Kendricks pulled out of the Tokyo Games because of a positive COVID-19 test.

The news about Kendricks – a two-time world champion and the American record holder – deprived the meet of one of its high-profile athletes, then rippled across the sport, which was scheduled to open less than 24 hours after the announcement.

He was one of dozens of athletes on the training track this week, and Australia announced it had put its entire 54-person team (41 athletes and 13 officials) in isolation and subjected it to testing after three athletes reported having casual contact with Kendricks.

A few hours after that, the Australian Olympic Committee announced the trio had tested negative and all but those three had been cleared to return to normal activities.

The three athletes remained in isolation, allowed to resume practice under strict distancing protocols. Australia said everyone was expected to be able to compete.

Shortly after Kendricks’ positive test was announced, another pole vaulter, Germán Chiaraviglio of Argentina, said he, too, was out because of a positive test.

It’s unclear how many other athletes might have had contact with Kendricks, how Olympic officials will figure that out, and what they might demand of them with the track meet only a day away.

The U.S. Olympic and Paralympic Committee didn’t offer details about Kendricks’ positive. A social media posting from his father, which was later deleted, said the 28-year-old from Mississippi, who is a member of the Army reserve, had tested positive but was feeling fine.

“We are following the USOPC and (local organizer’s) guidance on next steps to ensure the safety of the remainder of our delegation, and to offer support to Sam,” a statement from USA Track and Field said.

The pole vault world record holder, Sweden’s Armand Duplantis, said he was shocked to hear of Kendricks’ withdrawal. This was supposed to be one of the top showdowns of the meet. The first round is Saturday and the final is on Tuesday.

“As far as an hour ago I was still preparing myself for a big battle with Sam,” Duplantis said. “He’s one of my main rivals, and somebody who was definitely going to push me in the final.”

ROWING: Canada stormed to an early lead, then held off New Zealand over the final 200 meters to win the women’s eight gold medal, ending U.S. dominance in the event.

The Americans had won three consecutive gold medals but fell to fourth at the Sea Forest Waterway. They were dropped by the leaders early and were never in medal position.

China finished third for the bronze medal.

BEACH VOLLEYBALL: Americans April Ross and Alix Klineman moved into the knockout round after having just a little bit of trouble against the Netherlands.

Starting in a drizzle and finishing in a downpour, the No. 2 seeded Americans lost the opening set, 22-20. They trailed 12-9 in the second set before scoring four straight points and seven of the next eight to take it, 21-17.

In the tiebreaking set, they pulled away to beat the Dutch pair of Sanne Keizer and Madelein Meppelink, 15-5.

TENNIS: Novak Djokovic is into the medal rounds as he continues his quest for a Golden Slam.

The top-ranked Serb rolled past home favorite Kei Nishikori of Japan 6-2, 6-0 to reach the semifinals.

Steffi Graf in 1988 is the only tennis player to achieve the Golden Slam by winning all four Grand Slam tournaments and Olympic gold in the same calendar year.

Djokovic has already won the Australian Open, French Open and Wimbledon this year and needs the Tokyo Games title and the U.S. Open trophy to complete the Golden Slam.

In the women’s tournament, 12th-ranked Belinda Bencic of Switzerland and 2019 French Open finalist Marketa Vondrousova of the Czech Republic will meet in the gold-medal match.

Bencic beat Elena Rybakina of Kazakhstan 7-6 (2), 4-6, 6-3 and Vondrousova – who eliminated Naomi Osaka in the third round – defeated fourth-seeded Elina Svitolina of Ukraine 6-3, 6-1.

GOLF: Sepp Straka of Austria made four birdies in his last six holes for an 8-under 63 and a one-shot lead over Jazz Janewattananond of Thailand in the first round.

Thomas Pieters of Belgium, who finished one spot out of a bronze medal in Rio de Janeiro five years ago, shot 30 on the back nine for a 65.

Carlos Ortiz of Mexico also had a 65 in ideal scoring conditions on a course so pristine it didn’t have a divot when players first began arriving because it was closed for two months.

BASKETBALL: Japan’s bid for its first Olympic men’s basketball win in 45 years fell short despite a 34-point effort from Rui Hachimura.

Luka Doncic had another impressive performance with 25 points, seven rebounds and seven assists in 26 minutes, Zoran Dragic scored 24 points, and Slovenia remained unbeaten in its Olympic debut by beating Japan 116-81.

BASEBALL: Jeremy Bleich forced in the winning run by hitting batters with consecutive pitches in the 10th inning, and defending champion South Korea beat Israel 6-5 to win its Olympic opener.

Former Portland Sea Dogs catcher Ryan Lavarnway homered twice for Israel, which made its Olympic baseball debut, and Ian Kinsler also went deep.

Lavarnway tied the score 5-5 against former big league reliever Seunghwan Oh in the ninth inning with his second home run.

Kinsler’s two-run homer in the third and Lavarnway’s two-run drive in the sixth gave Israel a 4-2 lead.