Novak Djokovic warned on Friday that Rafael Nadal's humiliating Wimbledon defeat to Czech world 100 Lukas Rosol was a wake-up call for the game's superstars.
The world's top three players -- Djokovic, Nadal and Roger Federer -- have won 31 of the last 34 Grand Slam titles, a streak stretching back over seven years.
But Nadal's shock second round 6-7 (9/11), 6-4, 6-4, 2-6, 6-4 defeat to journeyman Rosol was the Spaniard's worst performance at a major since losing to Gilles Muller of Luxembourg at the same stage of Wimbledon in 2005.
"You cannot take anybody for granted," said defending champion Djokovic.
"You can't underestimate any opponent. I don't think Rafa did, he's well aware of the quality of all the players on the tour.
"But it's a Grand Slam. It's Wimbledon. Everybody wants to come up with their best game, especially when you're playing one of the top players.
"You have nothing to lose. You're out there on the court and you're going for your shots.
"It can serve as an example for everybody that anything is possible in this sport. Even though myself, Rafa, Roger, Murray, we've been dominant in Grand Slams, and it's expected of us to reach the last four.
"But tennis is improving. Everybody plays equally well."
Djokovic had a minor scare against another Czech on Friday in a third round match which was played, just like Nadal's, under the Centre Court roof.
The top seed dropped the first set against 33-year-old Radek Stepanek before easing to a 4-6, 6-2, 6-2, 6-2 win.
He goes on to play compatriot Victor Troicki, who put out Argentine 15th seed Juan Monaco 7-5, 7-5, 6-3, for a place in the quarter-finals. Troicki will be playing in his first last 16 tie at Wimbledon.
Friday's match was the second successive match under the roof for Djokovic after his second round win against America's Ryan Harrison.
For Nadal, the organisers' decision to close the roof on Thursday night, to allow the match to be completed, came when the world number two was back in the ascendancy, having taken the fourth set to level the match.
Play did not resume for 45 minutes as the roof closed and on the resumption, Rosol broke for a lead he would never relinquish.
"It distracted him a little bit because he was playing well in that fourth set," said Djokovic.
"But that's what happens. These are the conditions. You cannot affect the weather.
"Today we got to the court, they closed the roof, and then we saw sunshine and clear blue sky. I thought I played well under these conditions."
Djokovic found wily Stepanek, a quarter-finalist in 2006, hard to read in the first set as the Czech kept the champion pinned back by serving and volleying, almost an extinct technique on the slowing All England Club lawns.
But he won 18 of the next 24 games to storm to victory, taking another step closer to a sixth career Grand Slam title.
"I had break points in the first set but he came up with the big serves. It was a tough match, but I played really well in the second, third and fourth sets," said Djokovic.