LONDON - Novak Djokovic, Roger Federer, Stan Wawrinka and Andy Murray remain on course for the Wimbledon semi-finals ahead of 'manic Monday' when the last-16 takes place.
Serbia's Novak Djokovic returns to Australia's Bernard Tomic during their men's singles 3rd round match of the Wimbledon Championships, at the All England Tennis Club in southwest London, on July 3, 2015
Six of the top 10 seeds are safely into the business end of the tournament after a first week which saw seventh seed Milos Raonic and 10th-seeded Rafael Nadal defeated on court.
Fifth seed Kei Nishikori withdrew before the second round with a calf injury while eighth-seeded David Ferrer pulled out before the first round.
Defending Djokovic will face South African 14th seed Kevin Anderson in the fourth round, defending a 4-1 career lead.
Anderson won their first meeting in 2008 but since then it's been the world number one who has been on top winning the next four without dropping a set, including a straight sets win at Wimbledon in the second round four years ago.
"I think he is probably playing the tennis of his life," said Djokovic who hasn't dropped a set so far at the tournament so far and also captured the 2011 title.
"He's reached the highest ranking now in his career. He keeps on going forward.
"It will be a match of very small margins that will be decided by a few points. So I need to be able to get as many returns back in play."
Federer, 33, chasing a record eighth Wimbledon and 18th major, has dropped just one set so far, in his third round win over Sam Groth.
The Swiss, playing his 17th successive Wimbledon, faces Spanish 20th seed Roberto Bautista Agut who was voted the most improved player of 2014. He is in the fourth round for the first time.
However, he has lost both of his matches against Federer without winning a set including a fourth round loss to the Swiss at the 2014 US Open.
Murray, the 2013 champion tackles 36-year-old Ivo Karlovic, the oldest man to make the fourth round at the All England Club since compatriot Niki Pilic in 1976.
- Golden oldie Karlovic -
The 23rd seed is also the oldest to reach the last-16 of any of the four Grand Slams since 39-year-old Jimmy Connors at the 1991 US Open.
"It's a great feeling. I really like what I do. I'm just having fun. So if I'm able to do this at my age, it is unbelievable still," said Karlovic who has rained down 136 aces in three matches.
Murray needed treatment on his right shoulder in his four-set win over Andreas Seppi on Saturday but then reeled off the last six games of the match.
He will takes a 5-0 career lead into Monday's clash with Karlovic.
"It will be a very different match from Seppi. Ivo is going to be coming to the net a lot," said Murray.
"He's served very well, so the returns will have to be on if I want to get through that one."
Fourth seed and French Open champion Wawrinka faces Belgian 16th seed David Goffin who has made the fourth round at Wimbledon for the first time, equalling his previous best at a major when he came out of qualifying to reach the French Open last 16 in 2012.
Wawrinka has a 2-0 lead over Goffin with both wins coming on the hard courts of Chennai in 2011 and 2015.
American wildcard Denis Kudla is the lowest ranked player left in the tournament.
The world number 105 was winning a second-tier Challenger tournament at Ilkley in Yorkshire, northern England on the eve of Wimbledon.
Kudla is also the lone American standing but faces a stiff test against US Open champion Marin Cilic if he is to get to the quarter-finals.
The other last 16 matches feature Australia's Nick Kyrgios, who knocked out Nadal in the fourth round last year on his way to a maiden quarter-final, up against France's 2007 semi-finalist Richard Gasquet.
Vasek Pospisil, the world number 56, is only the fourth Canadian man to reach the last 16 and he faces Serbia's 22nd seed Viktor Troicki.
Troicki has reached the fourth round of a Slam for the first time since returning from a one-year doping ban in July 2014.
Czech sixth seed Tomas Berdych, the 2010 runner-up, takes on Gilles Simon, the French 12th seed who saw off compatriot Gael Monfils on Saturday in a match which began on Court One but was played to a conclusion under the lights of the Centre Court roof as darkness fell.