NEW YORK -- The US Open used its new, $150 million retractable roof atop Arthur Ashe Stadium during a match for the first time on Wednesday night.
Nadal had the distinction of hitting the first practice and match ball under the closed roof.
"I feel that the conditions are pretty similar when the roof is closed or open," Nadal said afterward.
The most noticeable difference was the amount of ambient noise -- chatter from spectators, mainly -- that could be heard during points.
U.S. Tennis Association executive director Gordon Smith said tournament organizers will look into that.
"This is New York. And yes, there's crowd noise. And yes, we want the crowds to come, we want them to be excited. We want them to cheer. And we think that over time, the fans will adjust and the players will adjust," he said. "It's obvious there's going to be more noise in a trapped environment than in an open environment."
Even before the roof was closed, chair umpire Cedric Mourier repeatedly implored spectators to keep quiet during points. Both Nadal and Seppi were surprised by just how many interruptions there were from fans, either moving around in the stands or simply being loud.
"The people, I think, are used to going to baseball [games] and keep talking," Seppi said. "There really was a lot of noise."
After dealing with rain delays and postponed finals for years, the USTA finally built a movable roof over its main stadium. It was available for this year's tournament, which started Monday, but the first two days were dry.
"It took well over 10 years to come up with a solution to do this that was affordable, was architecturally imaginative, that was cost-effective, that was efficient. But we did it," Smith said. "To see it work flawlessly was really incredible."
A light rain began to fall while Nadal and Seppi were playing. Tournament referee Brian Earley was monitoring the weather from off to the side of the playing surface and eventually walked over to chair umpire Cedric Mourier and the two players to let them know he wanted to shut the roof.
"This might take very few minutes,'' Mourier announced to the spectators. "Thank you very much for your patience."
Some fans applauded or cheered. Others pulled out their cellphones to shoot photos of the structure as it moved. Even Nadal took a glance overhead to sneak a peek.
ESPN tennis analyst Chris Evert took to Twitter to share her feelings on seeing the new roof in action.
The ROOF!!! Closed pretty fast! Love it!❤️❤️❤️— Chris Evert (@ChrissieEvert) September 1, 2016
In an interview with ESPN during its broadcast of the match, tournament director David Brewer said: "This is why we built the roof in the first place."
Asked what he thought of how things went Wednesday, Brewer replied: "Pretty sweet from my point of view."
The USTA has said that, based on pretournament testing, the expectation is there will be little difference in playing conditions, regardless of whether the roof is open or closed.
The only use of the roof until Nadal's match came when it was shut at the start of the tournament's opening ceremony on Monday night, then opened while Phil Collins sang "In the Air Tonight."
The US Open men's final was postponed in five consecutive years because of wet weather from 2008 to 2012.
"For a good show, for the comfort of the fans and for the fans in general [watching on] television," Nadal said about the new roof, "it's just an unbelievable improvement."
Information from The Associated Press was used in this report.