Daria Gavrilova has let a golden opportunity slip to move into the Australian Open third round, collapsing against Belgian Elise Mertens.

The Australian No.2 suffered a heartbreaking 7-5 6-3 loss after holding a 5-0 first-set lead.

With the match starting one minute before midnight – the latest ever at Melbourne Park – Gavrilova got off to a flyer, breaking Mertens twice.

She had four set points at 5-0 but was unable to convert and then missed another four opportunities as the Hobart champion edged her way back.

Gavrilova’s serve crumbled. The 23-year-old served 10 double faults for the match, while her unforced errors went through the roof with a total of 40.

The Australian was further rocked in the second set when trailing 4-2 she tried to challenge an incorrect ruling but umpire Aurelie Tourte said she was too late and had looked for the replay first.

“I raised my hand straight away,” Gavrilova said, with Toute replying: “No, you were waiting”.

Commentators described it as a “horrendous call”.

Mertens went on to win the game and although Gavrilova broke back, she was visibly upset and continued the argument with the umpire post match.

Gavrilova has enjoyed a stellar Open run, making the fourth round in the past two years, while this was Mertens’ Melbourne Park debut.