FLUSHING MEADOWS — It was an opening day like only New York can deliver.

Six former champions were in action Monday at the U. S. Open—Andy Roddick, Lleyton Hewitt, Kim Clijsters, Venus Williams and both defending champions, Serena Williams and Roger Federer.

The sky was a brilliant blue; the air, unseasonably cool and crisp for late August.

A record opening-day crowd of 36,085 was on hand, as well as one of the sport’s more beloved past champions, Andre Agassi, who was honored during evening ceremonies for his charitable work off the court.

And while no top seeds tumbled on this charmed afternoon, the future of American tennis took a beating.

Still, there was no shame in falling to the tournament’s presumptive favorites.

Alexa Glatch, 19, of Newport Beach, Calif., and Devin Britton, 18, of Brandon, Miss., drew the blessing and curse of opening play in Arthur Ashe Stadium — the world’s biggest tennis stadium — against the U. S. Open’s defending champions.

Serena Williams breezed past Glatch, 6-4, 6-1.

And Federer had only a minor hiccup against Britton, twice getting broken by the youngest player to win

the NCAA singles championship before advancing, 6-1, 6-3, 7-5.

“Tricky match for me,” Federer said, a measure of his generosity. “Playing a guy who’s got absolutely nothing to lose.”

Britton confessed afterward to being scared by the stage and his opponent.

And Federer, 10 years his senior, understood how he must have felt, having faced his own idol, Pete Sampras, on the grass lawn on Wimbledon when he had more ambition than achievements, and Sampras’ power was diminishing.

“All of a sudden I was in front of Pete Sampras at Wimbledon, and I couldn’t believe it, you know,” Federer said afterward. “If you admire a player, it doesn’t matter if he has lost first round many times, or he’s won many times the last year or so. It’s what he’s achieved and what you think of that player.”

Federer arrives at the 2009 U. S. Open with more trophies than he ever dreamed possible yet still hungry for more.

With a sixth consecutive U. S. Open title, Federer would extend his record of major singles titles to 16.

He would also claim his third major title of the year, although he didn’t have to face then-No. 1 Rafael Nadal en route to two of those (the French Open and Wimbledon).

Together, Federer and Nadal have won 17 of the sport’s last 18 majors (with Novak Djokovic breaking the chokehold at the 2008 Australian Open).

While Nadal missed two months this summer to address tendinitis in both knees, Federer has rarely looked more sharp or in command than he has these last few weeks, cruising to victory in a hardcourt tournament in Cincinnati that featured the top five players in the world.

Asked what drives him, now that he has reclaimed the No. 1 ranking, finally won the French Open and broken Sampras’ all-time mark of 14 majors, Federer paused and asked if the question could be repeated. The notion of having to create reasons to win was utterly alien.

The pursuit, he suggested, was its own reward.

“To try to win again and again,” Federer said. “I like being the winner of any tournament in the world. That’s why when I enter, I try to win. If I don’t, OK.

“I was away. I know tennis is not everything, so it’s not a problem. But if I enjoy playing tennis, why should I stop just because I’ve beaten the all-time grand slam record. That’s not what tennis is about.”

Serena, 27, has taken a markedly different approach to the sport this past year, producing her best when a major title is at stake and delivering considerably less otherwise.

Her record in the three grand slam events this year is 18-1; she is 20-9 in other tournaments.

But she strode onto Arthur Ashe Stadium — her favorite venue, to play before her favorite crowd — dressed to dazzle in a hot pink dress with a flared hem trimmed in black and proceeded to play as if impatient to get to the title match.

A three-time U. S. Open champion, Serena would match Billie Jean King’s record of 12 major singles titles if she wins a fourth U. S. Open.

“She can really step into a ball, that’s for sure,” said Glatch, who was addled by swirling winds and thrown by the enormous venue.

Meanwhile, Venus Williams was quite close to losing in the U. S. Open’s first round for the first time. She shrugged off a bad knee and came all the way back from a set and a break down to beat 47th-ranked Vera Dushevina of Russia, 6-7 (5), 7-5, 6-3, on Monday night.

Kim Clijsters — in her first grand slam event since 2007 — sailed past Viktoriya Kutuzova of the Ukraine, 6-1, 6-1.

Also advancing on the men’s side were Americans James Blake and John Isner.