Federer, after losing his No. 1 ranking to Rafael Nadal last year, won the 2008 U.S. Open, then put together back-to-back Euro Slams in Paris and London. Williams, who has failed to win any of the 13 Sony Ericsson WTA Tour events in which she's played the past 15 months, nevertheless managed to hoist the 2008 U.S. Open trophy, followed by triumphs this year at the Australian Open and Wimbledon.
Federer and Williams, the defending champions, will be the favorites at this year's U.S. Open, which begins on the last day of August. But that doesn't mean they will necessarily repeat as champions.
Mary Joe Fernandez, the U.S. Fed Cup captain and ESPN analyst, believes there are too many moving parts in tennis to hastily pencil in Federer and Williams as winners.
Last week, Fernandez called the match in Stanford, Calif., in which Samantha Stosur beat Serena in the quarterfinals. On Sunday, she watched Marion Bartoli, of all people, handle Venus Williams in a three-set final. On Monday, Fernandez was chasing her two children -- Isabella, 7, and Nicholas, 4 -- around a playground in Cleveland.
"Upsets can definitely happen -- we saw it at Stanford," Fernandez said. "I would still say the defending champions will be the favorites in New York, but there's a lot more depth than there's ever been, and everybody's improved so much.
"Eventually, they could have a bad day. In a Slam, that can be fatal."
That's why they call it Open Season.
It's been a month since Federer outlasted Andy Roddick 16-14 in the fifth set of the Wimbledon final; a month since Serena prevented her older sister from winning a third consecutive title at the All England Club. In that time we haven't seen anything to suggest that the favorites will absolutely, positively triumph in New York. In fact, the meager evidence suggests just the opposite.
Federer has been frolicking at home in Switzerland with the twin daughters, Charlene Riva and Myla Rose, which his wife, Mirka, delivered on July 23. The timing, another example of Swiss precision, gives Federer time to enjoy his new family and, one suspects, prepare diligently for the oncoming North American hard-court season.
Nadal, who lost his first match ever at Roland Garros (to Robin Soderling in the fourth round) and pulled out of Wimbledon with tendinitis, has been playing practice sets in Mallorca, Spain. Although both men are scheduled to compete next week in the ATP World Tour 1000 event in Montreal, there have been reports that they both could pass. For the record, Fernandez thinks they'll both play.
The women, too, are getting serious. Nearly all of the top players will be in Cincinnati next week and Toronto the following week.
In the meantime, it's been a pleasant month of not-quite-prime-time tennis.
Twenty-one-year-old Sam Querrey reached three successive ATP finals, breaking through in the last one against qualifier Carsten Ball in Los Angeles. Querrey, who also advanced to the finals at Newport and Indianapolis, now has a career-high ranking of No. 26. He leads the U.S. Open Series with 115 points, 45 points ahead of Robby Ginepri and 70 ahead of the third-place Ball.
Nikolay Davydenko, meanwhile, won back-to-back clay titles in Hamburg, Germany, and Umag, Croatia. World No. 1 Dinara Safina -- who has reached three of the past six Grand Slam finals but lost them all -- was the winner in Portoroz, Slovenia, her third title of the year.
After yielding a total of only five games to Maria Sharapova and Elena Dementieva in Stanford, Venus Williams staggered to lose the final to Bartoli -- the unorthodox Frenchwoman who now leads the U.S. Open Series.
"There's more unpredictability in women's tennis than I've seen," said Anne Worcester, tournament director for Pilot Pen Tennis and the WTA's first CEO. "There is no doubt fans want unpredictability. They don't want to know who's going to win. And that's what we have in men's and women's tennis today."
Still, after the brief hiccup of 2008, Federer is tennis's best answer to the constancy of death and taxes.
"With the improvement of all the young guys, Roger had to get better -- and he did," said Paul Annacone, head coach of men's tennis for Britain's Lawn Tennis Association. "That, to me, is very impressive. Now we're seeing how great Roger truly is."
The Wimbledon title was Federer's 15th major, breaking Pete Sampras' record. The U.S. Open offers another tantalizing slice of history.
On eight occasions in the Open era, men have won the same ATP-level tournament five years in a row (see chart), but no one has won six successive times. Federer, who saw Nadal end his Wimbledon streak at five a year ago, is eyeing the never-accomplished six-peat. Nadal, Andy Murray, Novak Djokovic, Roddick and Juan Martin del Potro may have other ideas.
"That's what makes it so exciting," Annacone said. "With a hopefully healthy Rafa back and a hungry Murray and an improving Djokovic, it's really lining up as an exciting time."
Greg Garber is a senior writer for ESPN.com.