Pete Sampras believes "bull" Novak Djokovic is playing some of the greatest tennis of all time after the world number one completed a career Grand Slam by winning the French Open.
Djokovic joined an elite group of eight men to have won all four majors when he beat Andy Murray to claim an elusive first title at Roland Garros on Sunday.
The sublime Serbian also became the first man since Rod Laver back in 1969 to hold all four majors at the same time and took his tally of grand slam triumphs to 12.
Djokovic has cemented his standing as the best in the business and legendary American Sampras has showered praise on the all-conquering 29-year-old.
The 14-time grand-slam champion told Omnisport: "He's at the top of his game, he's figured it out, this two-three year run has been some of the best tennis in the history of the game.
"What he's been able to do against Roger [Federer] - beating him four times; two at Wimbledon and two at the [US] Open, he's done it all.
"[It's] some of the greatest tennis of all time. Every tournament he's played in he's got to the final. It's mind-boggling these numbers he's putting up.
"He's very talented, he's the best mover in the world, he fights hard, he's got great strokes, serves big. He has the whole package and mentally he's a bull, it's just been amazing and I didn't see it coming.
"I always felt like Novak was up and down emotionally, but now he misses a shot and he's like boom, he misses a shot and he's back into it.
"It's fun to watch, I know he doesn't have quite the presence of a Roger or Rafa [Nadal], but I admire what he's been able to do and be so consistent."