ESPN 2008 US Open

NEW YORK -- He made his way easily through the players' lounge early last week, making small talk and slapping a few hands. He swept some of his long, brown hair behind his ear. There was no dazzling regal aura, no entourage.

Roger Federer may be the best tennis player in the history of the game, and Sunday's third-round, straight-sets victory over Radek Stepanek was his 30th consecutive match win here at the U.S. Open. Federer is looking for his fifth straight title, something last achieved by Bill Tilden -- 84 years ago.

Listening to the buzz around the lush grounds at the Billie Jean King National Tennis Center, you would never know it.

Rafael Nadal, who beat Federer in the finals at Roland Garros and Wimbledon, has drawn most of the attention. The New York tabloids have invested a good deal of energy in documenting the relationship between Novak Djokovic, who handled Federer easily in the semifinals of the Australian Open, and Paraguayan javelin thrower Leryn Franco. The wide-open women's field is another popular topic of discussion.

Federer hasn't been ignored, of course, but his quest has been underplayed. In fact, most stories about the new world No. 2 contain the words "vulnerable" and/or "no longer invincible."

"If I were to win a big tournament again, one of those Slams," Federer said, "right away I have the invincibility factor again, which is great for me.

"That's what I'm working for. I was that close in Wimbledon, so I hope to go a step further and win it this time."

Now, step back from the New York-minute mentality for a moment. This is the larger question that looms over Federer's quest: How many more major titles does Federer have in him? Where, exactly, is he in the Grand Slam curve?

It is a popular parlor game here; feel free to play along at home.

Federer, who turned 27 in early August, has won 12 Grand Slam championships, two behind all-time leader Pete Sampras. A year ago, many people believed Federer would equal or surpass Sampras this year. Now that he has gone 0-for-3, the giddy predictions of 17 or 18 majors have been revised.

An unofficial poll of the yawning media room quickly established a firm over/under: three. Some believers were willing to go as far as four -- or five -- while the cynics place the number at one -- or, in one case, none.

Matt Cronin of TennisReporters.com, USA Today's Doug Robson and Neil Harman of the Times of London all said they believed Federer would win three more Grand Slams.

"You know the Sampras timeline, right?" Cronin asked. "He won three after he turned 27. That sounds about right for Roger."

Said Harman, "In the end, I think he beats Pete -- barely."

John McEnroe, a CBS analyst, also thinks Federer will break Sampras' record.

History suggests it is quite doable.

No fewer than seven men won three or more majors after their 27th birthday. Rod Laver and Andre Agassi demonstrated remarkable longevity in winning five apiece, while Ivan Lendl, John Newcombe and Ken Rosewall managed four. Sampras and Jimmy Connors are at three.

It is an exceedingly tricky calculus with many, many variables. Here are three major items to consider:

• Peace of mind (and body): A bout with mononucleosis cost Federer 20 days of practice early this year, and clearly, he is still feeling the aftereffects. If Federer was finding it difficult to generate enthusiasm after four years as the No. 1-ranked player, going forward, this season should provide more than enough. Federer has stated a desire to play for four or five more years, which means he probably has 12 to 15 legitimate chances remaining to win a major.

• The big two: Nadal punishes opponents, but his body also suffers. The torque on his shots and the number of matches he plays leaves you wondering how long his joints will survive. Djokovic gets out of control sometimes, which leads to awkward landings and hyperextensions. If either player needed to take six months off, Federer could conceivably collect one or two Slams, perhaps even the French Open.

• The youth movement: There is a wave of young, gifted players coming up. As Federer's game diminishes, when will Andy Murray (21), Jo-Wilfried Tsonga (23), Juan Martin Del Potro (19), Marin Cilic (19) and Kei Nishikori (18) surpass him? How many Slams will they prevent him from winning?

The wild card in all of this is Federer's bout with mono. It is impossible to know how much of a factor it has been in Federer's indifferent season. Would those 20 days of practice have made him a few points better in that Wimbledon final? Might they have given him a marginally better training base here at the end of the year?

As it is, Federer is in remarkably good form. In eight previous sets with Stepanek, five went to a tiebreaker. On Sunday, Stepanek didn't even get a sniff. The 6-3, 6-3, 6-2 match was completed in a tidy 96 minutes.

Federer is serving quite well (45 aces), having been broken once in each of his three matches. Moreover, he is the tournament's leading man with respect to the return game, winning 13 of 32 games (42.5 percent).

This is the man, after all, who has reached 17 consecutive Grand Slam semifinals, a record so staggering it is difficult to imagine its demise. It would be a surprise if Federer doesn't make it 18; the three men standing in the way are, first, Igor Andreev in the fourth round and, presumably, the winner between Nikolay Davydenko and Gilles Muller in the quarterfinals. Djokovic would be the likely semifinal opponent, a delicious rematch to contemplate.

These are strange times for Federer. He seems to have crossed over from receiving polite respect from the spectators here to being the genuinely sentimental crowd favorite. On Monday night, when the USTA brought back the great champions from the past, Federer got the warmest reception.

Federer was asked by veteran correspondent Bud Collins what the low point of his season was.

"I never felt terrible, to be honest," Federer said. "Because every time maybe things weren't looking that great, either I was in [the] final of a Slam or I was able to win a tournament, like in Estoril or in Halle.

"So I guess I always had sort of a good spirit. I was working out hard. I was in practice and never really down. I think when you feel it most, when you go out on the practice court and you wonder what you want to do or change, and I never really felt I had that.

"That's a good thing, and I think that's why I'm always very, very positive, still, right now."

Greg Garber is a senior writer for ESPN.com.