Carlos Alcaraz survived a major scare in his Wimbledon opener while Aryna Sabalenka kept her cool to cruise into the second round on the hottest opening day in the tournament's history.

Temperatures at the All England Club on Monday topped 32 degrees Celsius, surpassing the previous record for the start of the tournament of 29.3 Celsius set in 2001.

Alcaraz ignored the sweltering conditions, digging dip for a 7-5, 6-7 (5/7), 7-5, 2-6, 6-1 win over 38-year-old Fabio Fognini in a gruelling clash lasting four hours and 37 minutes on Centre Court.

Alcaraz shrugged off an inconsistent display including 62 unforced errors as the world number two refused to wilt in the heat.

"I don't know why it is probably Fabio's last Wimbledon because the level he has shown shows he can still play for three or four more years," said the Spaniard.

During the match, the 22-year-old rushed to help a spectator who had collapsed in the stands, handing over a bottle of water as medics came to the woman's aid.

Alcaraz, who has never lost in a Grand Slam first round in 18 appearances, faces British qualifier Oliver Tarvet in the second round.

Top seed Sabalenka used ice packs to beat the heat during her 6-1, 7-5 victory over Canadian qualifier Carson Branstine on Court One.

The 27-year-old Belarusian is a three-time Grand Slam champion but suffered agonising three-set defeats in this year's Australian Open and French Open finals.

The world number one has never been beyond the Wimbledon semi-finals and missed last year's tournament with a shoulder injury.

Two-time Wimbledon finalist Ons Jabeur broke down in tears before retiring from her first-round match against Viktoriya Tomova.

Tunisia's Jabeur was trailing 7-6 (7/5), 2-0 when she brought a premature end to her clash with the Bulgarian world number 111.

The 30-year-old, beaten in the 2022 and 2023 Wimbledon finals, wiped away tears after losing a long fifth game in the first set and took a lengthy medical timeout.

Former US Open champion Daniil Medvedev, a Wimbledon semi-finalist for the past two years, suffered a meltdown against France's Benjamin Bonzi.

Bonzi won 7-6 (7/2), 3-6, 7-6 (7/3), 6-2 in three hours and seven minutes, with the fuming Russian smashing his racquet against his chair at the end of the match. (AFP)