20-time Grand Slam champion Serena Williams received lofty and heartfelt praise for her doggedness from John McEnroe on Thursday, as the three-time Wimbledon champion spoke in a conference call to promote ESPN’s coverage of this year’s Championships.

“To me, she’s like the greatest,” McEnroe said. “I’ve never seen someone come back from behind as much as she has. I can’t believe she’s got this will and belief at like really critical times. That tells you something about how incredible she is.”

McEnroe compared Williams’ intestinal fortitude to that of Rafael Nadal, and said he was blown away by the fact that Williams has now come back to win at a Grand Slam 33 times after dropping the first set (she owns a 33-32 record at majors when dropping the first set).

“To maintain that belief is something that is like a gift,” he gushed.

“Sometimes she comes out maybe not 100% fully engaged,” 18-time major champion Chris Evert added. “She kind of cruises along. Then it hits her, like her pride, ‘I don’t want to lose this match. I don’t want to lose this match. It’s not going the way I want it to go.’ For some reason she’ll start slapping some winners, she’ll give you that scream, then she’s won the match. How she digs herself out of holes, I think she gets mad at herself, and that is the motivation, that gets her going.”

McEnroe added that Serena has improved her ability to get out of tough situations as she has gotten older. “Serena has seemed late in her career to be mentally tougher than she’s ever been,” he said. “She’s been awfully tough at times. That’s very rare that you can be that consistently solid when it’s crunch time.”