updated 6:35 p.m. ET March 7, 2008

Pete Sampras was hardly at the height of his powers when he handed Roger Federer the keys to Centre Court at Wimbledon, losing their only head-to-head encounter that counted.

Sampras would go on to win only one more match at the All England Club after that 2001 defeat, never coming close to adding to his seven championships at the grass-court Grand Slam.

Federer, a decade younger, would go on to supplant Sampras at No. 1 in the rankings, assume Pistol Pete’s status as a perennial power at Wimbledon with five consecutive titles there, and begin to chip, chip, chip away at his record for major trophies.

So perhaps fair’s fair, considering that Federer has been, well, rather un-Federer-esque heading into his latest exhibition match against Sampras, which is Monday night at New York’s Madison Square Garden.

Yes, Federer actually is on a rare losing streak. The Swiss star was upset in the Australian Open semifinals in January — preventing him from adding to his 12 Grand Slams, two shy of Sampras’ total — and then in the first round of a tournament in Dubai this month.

That’s right. Gasp! Two consecutive losses.

“I think it’s a cause of concern for Federer, to be honest,” U.S. Davis Cup captain Patrick McEnroe said. “To me, it’s really big that these guys go out there and don’t seem to be intimidated by Federer and have sort of figured out that if you play consistently and can run a lot of balls down and make Federer hit a lot of shots, that you can beat him. Certainly, I wouldn’t say it’s a crisis for Federer. But I’d say that his days of utter domination may be coming to an end.”

An explanation emerged Friday, though: It turns out Federer was diagnosed in February with mononucleosis, an infection caused by a virus with symptoms that include fever, sore throat, headaches and feeling tired.

“This gave him a reason for why he wasn’t able to move and why he wasn’t able to recover,” said Federer’s agent, Tony Godsick. “It was annoying for him to not have reasons for why his body wasn’t responding.”

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Sampras, who beat Andre Agassi in the 2002 U.S. Open final in his last professional match, paid quite a compliment recently by comparing tennis’ current top player, Federer, to its former standard-bearer, himself.

“He’s got a good perspective. Doesn’t get too high or low on losses or wins. You know, just sort of has that attitude that I had: single-minded focus,” Sampras said. “He just goes out there and wins.”

And make no mistake: While there’s no Grand Slam championship or winner-take-all cash prize on the line Monday, that drive could very well be on display.

“He’s not going to want to lose; I’m not going to want to lose,” Sampras said. “That’s what people are coming to really see. It’s not us doing cartwheels. It’s about me serving 130 (mph) on the line.”

After all, for the two of them, just as for the more than 19,000 people who will be in the arena and however many might be watching live coverage on the Tennis Channel, it represents a rare instance of a “Who would win?” argument coming to life.

Tiger Woods vs. Jack Nicklaus.

Mike Tyson vs. Muhammad Ali.

It just does not happen often.

“There’s going to be a never-ending debate about who is the best or who would have done what against people from the previous era. We can talk about this for days and not come to a conclusion. That’s part of why this match is attracting a lot of attention and a sellout crowd,” said Ivan Lendl, who won eight Slam titles and is helping promote Monday’s event.

“They didn’t get to the top of the field in their time — and most likely top two or three or four all-time — by not being competitive,” Lendl said in a telephone interview. “So, yes, there may be a little lightheartedness, but at the end of the day, I think both will want to win rather urgently.”

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