New mum Victoria Azarenka continued her comeback bid for Wimbledon glory as Kei Nishikori and Johanna Konta ground out victories to reach the third round.
Andy Murray, Rafael Nadal and Venus Williams were made to sweat it out waiting on a sweltering day at the All England Club where players battled soaring temperatures and flying ants in their bid to make the last 32.
Former World No.1 Azarenka, playing her first Grand Slam tournament since giving birth to first child Leo in December, knocked out Russian 15th seed Elena Vesnina.
The 2012 and 2013 Australian Open champion, in her fourth match back, won 6-3, 6-3, taking her record over the Russian to 8-0 without dropping a set.
The Belarusian, 27, could become the first mother to win the Wimbledon singles since Evonne Goolagong Cawley in 1980.
"Travelling is a little stressful for me, travelling with a baby. I want to make sure that everything is okay. But overall, it's just great. It's really fun that I'm able to go home and spend time with my son," she said.
Azarenka next faces British wildcard Heather Watson who also upset the form book. The world No.102 downed Latvian 18th seed Anastasija Sevastova in straight sets.
British sixth seed Konta reached the Wimbledon third round for the first time with a marathon 7-6 (8/6), 4-6, 10-8 win over Donna Vekic which left her opponent in tears.
Konta and Watson's victories made it the first time that two British women have reached the last 32 at their home Grand Slam since Jo Durie and Anne Hobbs in 1986.
British men's defending champion Murray was facing the unpredictable serve-volleyer Dustin Brown on Centre Court, with Nadal due afterwards in the 15,000-seater arena.
Nadal, the 2008 and 2010 champion, is looking to reach the third round for only the second time since he finished runner-up in 2011 when he faces fellow left-hander Donald Young of the United States.
Fresh from winning a historic 10th French Open, Nadal is looking bury memories of the 2015 second round defeat to Brown, his last appearance at the All England Club.
Nishikori dug deep to keep his Wimbledon hopes alive as the Japanese ninth seed ground out a 6-4, 6-7 (7/9), 6-1, 7-6 (8/6) win over Ukrainian qualifier Sergiy Stakhovsky.
Despite reaching at least the quarter-finals of the other three Grand Slams, Nishikori has never been beyond the fourth round at Wimbledon.
He next faces Spanish 18th seed Roberto Bautista Agut who ousted German qualifier Peter Gojowczyk.
France's Jo-Wilfried Tsonga, the 12th seed, made short work of Italian qualifier Simone Bolelli in the sizzling heat, winning in straight sets.
Fans shielded their faces from the sun with towels, programmes and napkins as temperatures reached 29 degrees Celsius (84 degrees Fahrenheit).
Tsonga was one of several players bothered by an invasion of flying ants.
"That was strange… it was in my nose and in my ear," he said.
Gilles Muller won a gruelling five-set encounter with Czech qualifier Lukas Rosol. The 16th seed from Luxembourg won the decider 9-7.
US 24th seed Sam Querrey and Britain's Aljaz Bedene also won their second round matches.
Meanwhile seventh seed Marin Cilic, the 2014 US Open champion, was battling Germany's Florian Mayer for a spot in the third round.
Five-time champion Williams is trying to concentrate on tennis against the backdrop of the impending legal action she faces back home in the United States over a fatal car crash.
The 37-year-old veteran, devastated by the incident, broke down in tears on Monday when talking about the crash.
She was facing Chinese rising star Wang Qiang on Court One.
Czech 22nd seed Barbora Strycova lost to Japan's Naomi Osaka, who awaits Williams or Wang.
Two-time champion Petra Kvitova, the bookmakers' title favourite, continues her comeback from six months out recovering from a horrific knife attack in her home with a match against Madison Brengle of the United States.
Eighth seed Dominika Cibulkova and 27th seed Ana Konjuh of Croatia will face each other in round three after coming through their last 64 matches.
French Open champion Jelena Ostapenko and second seed Simona Halep were among those waiting to start their matches.