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UNITED STATES - MARCH 11: Roger Federer of Switzerland returns the ball to Pete Sampras of the U.S. during a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena. (Photo by Robert Caplin/Bloomberg via Getty Images)

UNITED STATES - MARCH 11:  Roger Federer of Switzerland returns the ball to Pete Sampras of the U.S. during a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena.  (Photo by Robert Caplin/Bloomberg via Getty Images)

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UNITED STATES - MARCH 10: Fans fill Madison Square Garden as they watch a best-of-three-set exhibition match between Pete Sampras of the U.S. and Roger Federer of Switzerland at MSG in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena. (Photo by Robert Caplin/Bloomberg via Getty Images)

UNITED STATES - MARCH 10:  Fans fill Madison Square Garden as they watch a best-of-three-set exhibition match between Pete Sampras of the U.S. and Roger Federer of Switzerland at MSG in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena.  (Photo by Robert Caplin/Bloomberg via Getty Images)

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UNITED STATES - MARCH 11: Roger Federer of Switzerland, left, shakes hands with Pete Sampras of the U.S. during after a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena. (Photo by Robert Caplin/Bloomberg via Getty Images)

UNITED STATES - MARCH 11:  Roger Federer of Switzerland, left, shakes hands with Pete Sampras of the U.S. during after a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena.  (Photo by Robert Caplin/Bloomberg via Getty Images)

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UNITED STATES - MARCH 11: Pete Sampras of the U.S. serves to Roger Federer of Switzerland prior to a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena. (Photo by Robert Caplin/Bloomberg via Getty Images)

UNITED STATES - MARCH 11:  Pete Sampras of the U.S. serves to Roger Federer of Switzerland prior to a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena.  (Photo by Robert Caplin/Bloomberg via Getty Images)

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UNITED STATES - MARCH 11: Pete Sampras of the U.S. returns the volley to Roger Federer of Switzerland during a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena. (Photo by Robert Caplin/Bloomberg via Getty Images)

UNITED STATES - MARCH 11:  Pete Sampras of the U.S. returns the volley to Roger Federer of Switzerland during a best-of-three-set exhibition match at Madison Square Garden in New York, U.S., on Monday, March 10, 2008. Federer, the world's No. 1-ranked player, defeated Sampras, who won a record 14 Grand Slam singles titles before retiring from the men's tennis tour, 6-3, 6-7 (4-7), 7-6 (8-6) on a hard-court surface at the indoor Manhattan arena.  (Photo by Robert Caplin/Bloomberg via Getty Images)