Roger Federer and Serena Williams both won their first-round singles matches on a day temperatures soared at Wimbledon.
Swiss top seed Federer, who is 37 in August, began his bid for a record-extending ninth men's title with a 6-1 6-3 6-4 win over Serbia's Dusan Lajovic.
American Williams, 36, battled blustery conditions to reach the second round with a 7-5 6-3 victory over Dutchwoman Arantxa Rus.
British wildcard Katie Swan reached the second round for the first time as she beat world number 36 Irina-Camelia Begu 6-2 6-2.
A packed Centre Court was dominated by Federer fans - wearing branded hats and clothing, and faces painted with Swiss flags.
The world number two's supporters were rewarded with a clinical performance by 20-time Grand Slam winner Federer, who needed just 79 minutes to see off Lajovic.
"I felt good from the start, which was not the case when I played him last year," Federer told BBC Sport. "I felt at home."
Seven-time champion Williams, playing her first match at the All England Club since 2016, did not quite progress so easily.
"I'm happy to get through that. I didn't play my best but I will get there," said Williams, who is returning after the birth of her first child.
US Open champion Sloane Stephens and fifth seed Elina Svitolina were the biggest casualties on the opening day.
American Stephens lost 6-1 6-3 to world number 55 Donna Vekic of Croatia while Svitolina fell to Germany's world number 57 Tatjana Maria 7-6 (7-3) 4-6 6-1.
Stephens out in shock first-round defeat - Best Shots
Five-time winner Venus Williams overcame a sluggish start to clinch a 6-7 (3-7) 6-2 6-1 victory over Sweden's Johanna Larsson but second seed Caroline Wozniacki of Denmark only needed 59 minutes to beat American Varvara Lepchenko 6-0 6-3.
Poland's Agnieszka Radwanska, the 2012 runner-up, then supplied the late night drama, saving six match points to beat Romanian qualifier Elena-Gabriela Ruse 6-3 4-6 7-5.
Men's third seed Marin Cilic, the 2017 runner-up, eased to a comfortable 6-1 6-4 6-4 win over Japan's Yoshihito Nishioka, while three-time Grand Slam champion Stan Wawrinka, now ranked 224th because of injury, overcame sixth seed Grigor Dimitrov in four sets.
Croat Ivo Karlovic, 39, and Russian Mikhail Youzhny, 36, treated Wimbledon fans to the oldest Grand Slam match since 1978 in the first round on Monday. The pair had an an average age of 37 years and eight months.
Katie Swan storms to win over Begu - Best Shots
Two-time Wimbledon champion Andy Murray withdrew from the tournament with a "heavy heart" on Sunday.
The 31-year-old Scot said it was "too soon" to play five-set matches after his comeback from hip surgery, so the British challenge in the tournament would have to come from elsewhere.
That baton was initially taken up by 19-year-old Swan, who defied her ranking of 204th in the world to claim an impressive straight-set victory against 27-year-old RomanianBegu in 56 minutes on Court 14.
Harriet Dart, 21, gave seventh seed Karolina Pliskova of the Czech Republic a scare but her Wimbledon debut ended in a 7-6 (7-2) 2-6 6-1 defeat.
Fellow wildcard Liam Broady was beaten 7-5 6-0 6-1 in the men's singles by Canada's Milos Raonic while Slovenian Aljaz Bedene beat Cameron Norrie 4-6 7-6 (7-4) 7-6 (7-4) 6-4 in a gruelling match.
The tournament's official bird scarer Rufus - a Harris Hawk tasked with frightening pigeons away from the courts - had to be doused in water to cool off
Temperatures on day one at the All England Club touched 30C as fans were drenched in glorious sunshine.
The hottest recorded day at Wimbledon came in 2015, when thermometers registered a scorching 35.7C - breaking a record which had stood since 1976.
With the current heatwave forecast to continue over the next fortnight, that may well be broken.
If the temperature is above 30.1C, female players are allowed a 10-minute break in between the second and third sets, but there is no such rule for the men.
Among the victors on day one was American Sam Querrey, who beat Australia's Jordan Thompson 6-2 6-4 6-3.
The 30-year-old, who got married to Abby Dixon last month, said he had postponed his honeymoon plans to step up his grass-court preparations for Wimbledon.
"We went home for three days and flew over for Queen's, if you count that as a honeymoon!" he said.
"I don't think Abby does. Maybe at the end of the year, we will do a honeymoon somewhere close to where we live."
Possibly one of the most bizarre moments of the first day came from Frenchman Gael Monfils, who challenged his own serve, which was called in, against compatriot Richard Gasquet.
British number one Johanna Konta, a semi-finalist last year, will open proceedings on court two on Tuesday.
She takes on Russia's Natalia Vikhlyantseva, who is ranked 106th in the world.
Kyle Edmund, the British men's number one, is first up on Court One against Alex Bolt of Australia.
Defending women's champion Garbine Muguruza plays first on Centre Court, as tradition dictates, with Rafael Nadal and Simona Halep following.
England play Colombia in the last 16 of the football World Cup at 19:00 BST, and that match could clash with Britain's Heather Watson, who is fourth on court 12.