London: Injury-plagued Japanese star Kei Nishikori limped out of Wimbledon on Wednesday as top seeds Novak Djokovic and Serena Williams targeted quickfire wins to escape temperatures soaring to a brutal 34 degrees.
Fifth-seeded Nishikori had been scheduled to face Colombian world number 60 Santiago Giraldo on Centre Court for a place in the last 32.
But the 25-year-old admitted that the left calf injury he suffered last month in Halle, which had forced him to retire in the semi-finals, was still a factor during his five-set win over Simone Bolelli in the first round at Wimbledon on Monday.
"It got worse in the fifth set of that match, it hurt so much," said Nishikori. "It hurt to walk and run today so I decided not to play."
As Giraldo goes on to face either German teenager Alexander Zverev or American wildcard Denis Kudla for a third round spot, Nishikori was left contemplating another injury setback in his career.
Nishikori, the US Open runner-up last year, didn`t play from April 2009 until April 2010 after undergoing surgery on his right elbow.
Last year, he was forced to quit his Madrid Masters final against Rafael Nadal with a back injury which was still affecting him by the time the French Open came around.
With temperatures at Wimbledon at their highest since the record-breaking 34.6 degrees Celsius (94.28 degrees Fahrenheit) in 1976, the tournament heat rule was being used.
That allows for a 10-minute break between the second and third sets of women`s matches.
However, the rule does not apply to the men`s tour despite them having to slog it out over five sets.
All England Club chiefs also closed the Centre Court roof to keep the 15,000-capacity arena air-conditioned.
But it was reopened for the start of play at 1200GMT as organisers insisted on the integrity of the event as an outdoor grasscourt tournament being preserved.
Defending champion Djokovic was opening play against Finnish veteran Jarkko Nieminen.
World number 92 Nieminen is playing in his 12th and last Wimbledon, having ended the All England Club career of 2002 champion Lleyton Hewitt over five sets in the first round.
Djokovic, also the 2011 champion, has a 5-1 career record over the 33-year-old Nieminen, a quarter-finalist in 2006.
The last time Djokovic lost in the second round at a Grand Slam was at 2008 Wimbledon, when as number three seed he was defeated by Marat Safin.
Fourth seed and French Open champion Stan Wawrinka takes on world number 48 Victor Estrella Burgos, only the second Dominican Republic player to take part in a Grand Slam.
Wawrinka recorded his best Wimbledon performance by reaching the quarter-finals in 2014.
Seventh-seeded Canadian and 2014 semi-finalist Milos Raonic was facing German veteran Tommy Haas.
At 37 years and 100 days old, Haas is bidding to become the oldest man to reach the third round at a Grand Slam since Jimmy Connors, who was just past his 39th birthday when he made the last 32 at the 1991 US Open.
US Open champion Marin Cilic, the ninth seed, meets Lithuania`s Ricardas Berankis in a tussle between two former world junior number ones.
Five-time women`s champion and top seed Williams faces Hungary`s Timea Babos as she continues her bid to sweep a calendar Grand Slam and a 21st major.
Maria Sharapova, the 2004 champion and fourth seed, tackles Dutch qualifier Richel Hogenkamp.
In early second round matches, Bulgarian 11th seed Grigor Dimitrov defeated Steve Johnson of the United States 7-6 (10/8), 6-2, 7-6 (7/2), Belgian 16th seed David Goffin saw off Britain`s Liam Broady 7-6 (7/3), 6-1, 6-1 and French 21st seed Richard Gasquet got the better of compatriot Kenny De Schepper 6-0, 6-3, 6-3.
Australian 27th seed Bernard Tomic was a 7-6 (7/3), 6-4, 7-6 (7/5) winner over Pierre-Hugues Herbert of France.