NEW YORK – Champion at Wimbledon in both singles and doubles. Winner again at the All England Club in both events, four weeks later at the London Olympics.

Nobody would blame Serena Williams if she felt worn down by this year’s jam-packed tennis calendar. She doesn’t see it that way, though – even with the grind of the U.S. Open looming.

“I look forward to this,” Williams said. “It’s almost like a launching pad for what I want to do for the rest of the hard-court season.”

In a way, yes, today’s start of the year’s last Grand Slam actually marks something of a new beginning – the start of a six-month stretch on the hard courts that winds down at the 2013 Australian Open.

Call it mental gymnastics, a creative way of looking at things or whatever else might apply. What can’t be denied is that in an Olympic year, the U.S. Open – considered the toughest test in tennis – is essentially the season’s fifth major.

“A lot of them,” Jim Courier said, “are running on fumes.”

Indeed, many top players have had to double down on their fitness and find new ways of organizing their schedules to get ready for what they hope will be a two-week grind in the fishbowl that is Flushing Meadows.

Defending champion Novak Djokovic barely took any time off following his fourth-place finish at the Olympics. He traveled to Toronto for a hard-court tuneup, played six matches and won the tournament. Then, he flew to Cincinnati, played six more matches but lost to Roger Federer in the final.

No shame there, though that loss to Federer did include an uncharacteristic 6-0 whitewashing in the first set.

“Mentally, I wasn’t there, wasn’t fresh,” Djokovic said. “It had been a very busy time starting at the Olympic Games, and maybe that caught up with me at the end.”

Though the women’s game has been more in flux than the men’s of late the math is essentially the same in 2012: Three of the top four women – No. 1 Victoria Azarenka (Australia), No. 3 Maria Sharapova (France) and No. 4 Williams (Wimbledon) – have major titles this year and all need this one to break the tie.

Where things differ is in the way Williams has been playing of late. She lost a total of 17 games over six matches in the Olympics, punctuating it with a 6-0, 6-1 victory over Sharapova in the final.