The MLS Is Back tournament wasn’t a day old when it appeared as if the league would have to make a quick U-turn and leave Orlando, Florida. Two teams had been withdrawn from the tournament because 20 players tested positive for COVID-19 and several others had initial unconfirmed positive tests.

The league’s elaborate quarantine bubble at Disney’s Swan and Dolphin resort clearly had been stretched too thin to protect the 26 teams and 1,300 people MLS had crowded inside. Panic was beginning to set in.

“It’s as if they sent us to Wuhan in the middle of the pandemic,” Toronto FC defender Chris Mavinga told the French sports daily L’Equipe the day before his team’s tournament opener was postponed because players on both teams had inconclusive tests.

The league trotted out deputy commissioner Mark Abbott to change the narrative. MLS had confidence in its protocols, he said, and the league would soldier on.

“We believe the tournament can be carried out safely,” he said.

That was 16 days ago. Since then, the league says it has performed 7,615 tests without a confirmed positive. Abbott was right and the league’s return-to-play tournament, which once seemed on the verge of being canceled, has advanced to the knockout stages without a recent hiccup.

The National Women’s Soccer League also enjoyed success keeping COVID-19 at bay. The first professional sports league in the U.S. to resume play during the pandemic, the NWSL finished its eight-team 29-day tournament in suburban Salt Lake City Sunday without a single player or team official testing positive in its quarantine bubble.

Contrast that with Major League Baseball, which postponed two games Monday over a coronavirus outbreak. The Miami Marlins, who had 11 players and two coaches test positive, could have their season paused indefinitely.

“As we have seen with the current sports experiment, keeping this virus at bay — even with elaborate planning — can be difficult,” said Dr. Anne Rimoin, a professor of epidemiology at UCLA and director of the school’s Center for Global and Immigrant Health. “It hinges on perfect behavior and testing — both of which are hard to achieve.

“Most professional sports require some level of physical contact and it’s hard for these athletes to wear masks, so designing a perfect system is going to be tough unless everyone is 100% perfect at quarantining.”

MLS and the NBA, which had two players test positive since teams began checking into their protective bubble in Orlando earlier this month, apparently have gotten pretty close to perfect. The NBA will resume its season this week.

“The fact that we haven’t had any positive tests, it’s given some sense of calmness towards all the players in the bubble,” said LAFC midfielder Mark-Anthony Kaye, whose team was one of 16 to advance to the MLS tournament’s knockout stage. “So that’s a positive. But other than that, things are the same.”

The biggest problem with the bubble now, Kaye said, is boredom. Players can’t leave the hotel property other than for training sessions and games, and rarely leave their rooms since they have to wear masks and practice social distancing when they do.

“Guys are dealing with the mental part of it, away from their families and stuff,” he said. “That part doesn’t get easier with time.”

With the tournament in the elimination stages, the bubble is shrinking daily. By Wednesday, eight teams will remain. But MLS will face another, much larger, challenge when the competition ends Aug. 11.

The league plans to resume its season late next month with each team playing 18 games, nine on the road. That will necessitate the kind of travel that has tripped up MLB, especially since more than half of the soccer league’s 23 U.S.-based teams play in states averaging more than 1,000 new COVID-19 cases a day. Plus, the border separating those states from the three Canadian teams remains closed because of the virus until at least Aug. 21.

“Until we have a vaccine, I think there are going to be challenges with this,” said Dan Hunt, president of FC Dallas, which, along with Nashville SC, was forced to pull out of the MLS Is Back event. “This is kind of the reality of what has happened to us in 2020. I think you will see stopping and starting in some sports.”