Australian teenager Nick Kyrgios stunned Wimbledon tonight after beating world number one Rafael Nadal in a match even his own mother thought he would lose.
The 19-year-old produced one of the greatest shocks in the tournament's history by defeating the Spaniard in four sets on Centre Court.
Three-time Wimbledon champion McEnroe was so impressed by his performance that he believes he could emulate Boris Becker by winning the title in his teens.
Wild-card entrant Kyrgios arrived at Wimbledon ranked 144th in the world, and will now leave having reached at least number 65.
He revealed after the match that his mother, Norlaila, did not think he had the quality to beat Nadal.
"Last night I was actually reading a comment that she thought Rafa was too good for me," he said.
"It actually made me a bit angry. You would think he's in a whole other level compared to me. I just believed in myself that I could create some opportunities. I took them under pressure today."
He said he would send his mother a text message with a smiley face following his win.
Kyrgios also produced the shot of the tournament with a casual flick between his legs midway through the second set.
He seemed surprised with how the match went, posting a message on Twitter which simply read: "Erm, ok then..........."
Kyrgios wrote last week that he wanted 25,000 Twitter followers by the end of Wimbledon and he cracked the milestone mid-way through the match. He now has more than 36,000.
Nadal, 27, said: "The thing is this surface, when you have an opponent that he decides to serve and to hit every ball very strong, you are in trouble.
"I think that I didn't play really bad. But that's the game in this surface."
McEnroe, now commentating at the tournament for the BBC, reckons Kyrgios had the look of a champion about him as he demolished Nadal's title hopes.
"I could see it from the commentators' box, that he absolutely believed he was going to win this match, and he's acting to me like he can win this tournament.," McEnroe said.
"The last guy I saw like this is... Boris Becker, that young teenager, no fear whatsoever - 'no matter what comes my way I'm going to be better than them'."
Becker, at the age of 17, won Wimbledon in 1985, and triumphed again aged 18 and 21.
Kyrgios will play Milos Raonic in the quarter finals.
Meanwhile Judy Murray has hit out at parents with "more money and less time" for not encouraging their children to play sport.
The mother of reigning Wimbledon champion Andy Murray warned there are not enough young girls involved in tennis.
The 54-year-old said: "I loved all sports when I was young, I wanted my kids to enjoy sport so I was always playing actively with them, whatever they wanted to play.
"But it's not every parent that does that with their kids any more. It's much easier to hand them a DVD or a CD or something and sit and watch that.
"I think parents generally have less time - maybe more money and less time - so they are paying people to look after their kids and do the activity with them, rather than doing it themselves."
Nadal's loss was not the only shock of the day on Centre Court as Maria Sharapova was knocked out in three sets by fearless German Angelique Kerber.
Their matches were watched by a number of famous names in the Royal Box, including operatic singer Katherine Jenkins and her fiance Andrew Levitas, celebrity chef Michel Roux Jr and newsreader Fiona Bruce.
There was no need for the roof to be closed as two days of wet weather disrupting play were followed by glorious sunshine at SW19.
Serena Williams said she was "heartbroken" to have to pull out of Wimbledon through illness.
The 32-year-old managed only three games of her women's doubles match alongside sister Venus before being persuaded to call it day.
In scenes that were uncomfortable to watch on Court One, Serena was plainly not herself and seemed to be struggling with her vision.
She served four consecutive double faults as the sisters surrendered the third game of their match against German Kristina Barrois and Swiss Stefanie Voegele.
The Women's Tennis Association announced the official cause of the withdrawal as a "viral illness" for Serena.
Andy Murray is back in action tomorrow against Grigor Dimitrov as he continues his bid to retain the men's singles title.
But the Scot's mother revealed she is not finding it any easier watching him despite his success in 2013.
When asked if sitting in the players' box was less stressful than last year, Judy said: "No! I think there is a huge expectation level out there from everybody, obviously because he's won Wimbledon and he's won the US Open and the Olympics.
"I think everybody is expecting him to do well."