Djokovic two sets down

World number one and favorite Novak Djokovic is staring defeat in the face at Wimbledon as he trails American Sam Querrey in their third round contest.

Djokovic was edged out of a tight first set on a tie-break but collapsed to a 1-6 second set defeat to a player who has never beaten a world number one or gone beyond the fourth round at SW19.

Rain forced the players off, which rescued an out-of-sorts Djokovic, who is aiming to win a calendar Grand Slam and his fourth Wimbledon crown.

Wawrinka out

Former world number four Juan Martin Del Potro pulled off a shock second-round win over fourth seed Stan Wawrinka, beating the Swiss in four sets at Wimbledon.

Del Potro has missed over two years because of injury problems, sinking to world number 165 in the process. But there were no signs of rustiness as the Argentine recovered after dropping the first set to run out a convincing 3-6 6-3 7-6 (7-2) 6-3 winner.

Del Potro, a Grand Slam winner at the US Open in 2009, is in the same side of the draw as Andy Murray, and the victory over Wawrinka opens up the possibility of a semi-final showdown with the Briton.

"It feels amazing," Del Potro said after the match. "I beat one of the guys who is playing great tennis this season and I couldn't have expected this before today.

"I enjoyed the crowd, they were incredible and I'm very happy.

"It is my second or third career now after all the injuries. I was sad for the last two years and now I am enjoying playing tennis again. I feel alive."

Williams rolls on

Women’s reigning champion Serena Williams was made to sweat against compatriot Christina McHale, but eventually took it 6-7 (7-9) 6-2 6-4.

McHale, ranked 65th in the world, took the first set on a tie break but Williams roared back in the second to level the match with a series of pulverising forehands.

McHale made Williams work hard for the win, but Serena’s quality eventually shone through and the favorite sneaks through.

On another day interrupted by rain, which has led to the All England Club confirming play on the middle Sunday for the first time since 2004, five-time women's champion Venus Williams made it through to the fourth round by overcoming 29th-seeded Daria Kasatkina of Russia 7-5, 4-6, 10-8.

The match on Court One was delayed four times by rain, including once with Williams holding a match point at 7-6 in the third set. When play resumed, Kasatkina saved the match point and held to 7-7. Four games later, the eighth-seeded Williams broke to end the contest, with Kasatkina slapping a forehand into the net on the final point.

Nick Kyrgios survived a warning for bad language and a third set sulk to clinch a 6-7 (3/7), 6-1, 2-6, 6-4, 6-4 victory over German Dustin Brown in an explosive second round clash, to set up a third round match against Feliciano Lopez or Italy's Fabio Fognini.

Elsewhere, there were wins for John Isner, Lucas Pouille and Jo-Wilfried Tsonga, while German Benjamin Becker fell in straight sets to Tomas Berdych.