Reigning French Open champion Jelena Ostapenko has joined fellow top seed Kristina Mladenovic in suffering shock first-round exits at the Sydney International.

Fifth seed Mladenovic was trailing 6-4 4-2 to Australian wildcard Ellen Perez when she succumbed to fatigue during Sunday’s record-breaking heatwave.

However third seed Ostapenko, who is ranked No.7 in the world, became the second big-name to fall after falling 7-6 (6-3) 6-1 to Ekaterina Makarova.

The Latvian shot to stardom last year when she became the first unseeded player in the Open era to win at Roland Garros, defeating current world No.1 Simona Halep.

However she will now need to turn around her form heading into next week’s Australian Open, having also lost her tournament opener in China last week.

Earlier on Sunday, Perez defied scorching temperatures to claim her maiden WTA tour victory against the world No.11 Mladenovic in just her second tournament.

The world No.343 progresses to the second round where she is likely to face Australian No.1 Ashleigh Barty, who opens her campaign against qualifier Veronica Cepede Royg on Monday.

Fellow Australia hopeful Sam Stosur will also be in action, while top two seeds Garbine Muguruza and Venus Williams enjoy a first-round bye.

Defending women’s champion Johanna Konta faces Agnieszka Radwanska.