American Pete Sampras, who retired from tennis in 2002 after winning 14 Grand Slam titles, says Roger Federer is the best in history. (Elise Amendola/Associated Press)

If you ask Pete Sampras, Roger Federer earned the title of best tennis player in history even before he won the French Open.

Federer joined the American in the record books on Sunday when he won his first title at Roland Garros, making him the sixth man to complete a career Grand Slam sweep, and tying Sampras's record with the most Grand Slam titles ever at 14.

"What he's done over the past five years has never, ever been done — and probably will never, ever happen again," Sampras said. "Regardless if he won there or not, he goes down as the greatest ever. This just confirms it."

On hand to give Federer the French Open trophy on Sunday was Andre Agassi, the last player to complete a career Grand Slam sweep, in 1999.

"How do you sort of argue with his numbers? It's pretty incredible," Agassi said of Federer. "A lot of people say it's better to be lucky than good. I'd rather be Roger than lucky."

For a long time, Sampras pointed to his idol Rod Laver, 11-time Grand Slam champ, as the best tennis player in history. Laver was the last man to win all four Grand Slam titles in a single season, a feat he accomplished in both 1962 and 1967.

Laver was barred from competing in those tournaments from the time he turned professional in 1963 to the start of the Open era in 1968.

Federer is now Sampras's choice for best ever.

"Now that he's won in Paris, I think it just more solidifies his place in history as the greatest player that played the game, in my opinion," said Sampras, who retired in 2002.

"I'm a huge Laver fan, and he had a few years in there where he didn't have an opportunity to win majors. But you can't compare the eras, and in this era, the competition is much more fierce than Rod's."

Sampras added Federer will "go on and win a lot more" titles.

He gets his first chance to break Sampras's mark in two weeks at Wimbledon, which starts June 22.

With files from The Associated Press