Katie Boulter claimed one of the best victories of her career in the first round of the Australian Open over experienced Russian Ekaterina Makarova – twice.

A change in the rules for this tournament means matches that reach 6-6 in the deciding set will be finished by a first-to-10-points tie-break rather than the standard first-to-seven-points one.

Although the umpire reminded players and fans when the score reached 6-6 in the third set, Boulter was so focused she did not pay attention and celebrated exuberantly when she reached 7-4.

She walked to the net only to realise her mistake but reacted impressively to win 6-0 4-6 7-6 (10/6) after two hours and 24 minutes in oppressive Melbourne heat.

The 22-year-old from Leicestershire said: "I was in the moment and I kind of forgot it was first to 10 but I'm happy I could dig deep and get through it in the end.

"I ended up getting the win, I'd probably have been really devastated had I not. I can laugh it off now. At least I know the rule so it definitely won't happen again."

Boulter lost the next two points but then won three in a row to become the first British player through to the second round.

She said: "I think it's actually very tough, because you've just released and you think you've won the match, to get back to work and find a way. I thought I did that really well and I'm pretty proud of myself for digging deep."

This was a match that showed how far Boulter has come over the last year, climbing 100 spots in the rankings and beginning to establish herself as a genuine threat to higher-ranked opponents.

Makarova is a two-time grand slam semi-finalist, including here four years ago, and can boast 13 wins over top-10 players at the slams but Boulter crashed 53 winners past her and her mental strength was just as impressive as her shots.

Boulter would have to cause a huge upset to make it further, though, with 11th seed Aryna Sabalenka, who has been hotly tipped to challenge for the title, next up.

It was not such a happy start to the tournament for Heather Watson and Harriet Dart, who was handed the dreaded double bagel in a 6-0 6-0 loss to childhood idol Maria Sharapova on Rod Laver Arena.

Dart's under-powered serve took a pounding at the hands of the Russian, the champion here 11 years ago, and the young British player was left in tears afterwards.

The 22-year-old, who came through three matches of qualifying for the first time at a slam, said: "It was always going to be a difficult match, especially on such a big court. She's got a lot more experience than me but I came through qualifying so that's something to be positive about."

Sharapova was typically matter of fact when asked whether she felt for Dart, saying: "There is no time for that, I'm sorry to say."

The unwanted record of first player out of the tournament actually fell to Watson, whose disappointing form continued with a 6-1 6-2 loss to 31st seed Petra Martic.

The 26-year-old has found herself stuck in the tennis doldrums and admitted she was so tense on court that she felt faint and dizzy and had to call the doctor.

Watson said: "I haven't been like myself on court lately. I've got to change something. I'm not going to continue like this."