Serena Williams, Novak Djokovic headline U.S. Open field

In a year unlike any other, get ready for a U.S. Open unlike any other.

“There was definitely a point where, in the beginning, I was like: There is no way these tournaments can even happen,” Serena Williams said about playing amid a pandemic.

Professional tennis returned recently from a hiatus of nearly six months caused by the coronavirus outbreak — and it will be back on one of its biggest stages Monday, when New York begins hosting the first Grand Slam matches since the Australian Open in February.

“There are going to be a lot of people around the world who think we should not play tennis, that no public gathering should happen. I understand that fully. I really do,” said No. 1-ranked Novak Djokovic, who caught the coronavirus in June during an exhibition tour he organized in Serbia and Croatia that did not mandate mask-wearing or social distancing.

“But, you know,” he continued, “I think there also is going to be quite a lot of people that are going to be happy to see tennis keep going.”

The U.S. Tennis Association set up what it calls a “controlled environment.” Nearly all players and their limited-to-three entourages are staying in two hotels on Long Island (eight players opted for private housing at a cost of $40,000). They’re barred from going to Manhattan.

There’s frequent testing for the coronavirus. One player said she got a nose swab at 7 a.m., four hours before a match at the Western & Southern Open, the hard-court tournament that ended Saturday at the same site used for the U.S. Open — it’s usually played in Ohio.

There are dozens of “social distance ambassadors” tasked with making sure players and others are covering their mouths and noses and staying far enough apart.

“The protocols that they have are so...