Coco Gauff has reached the Australian Open semifinals for the first time, needing a gritty three-set win over unseeded Marta Kostyuk to advance to the last four.

The 7-6 (8/6), 6-7 (3/7), 6-2 victory on Rod Laver Arena was not a performance that would strike fear into Gauff's next opponent, either defending champion Aryna Sabalenka or ninth seed Barbora Krejčíková.

She made 51 unforced errors, five fewer than Kostyuk, had her serve broken seven times and recorded nine double faults.

But the effort after three hours and eight minutes on court, was enough for Gauff to keep her Australian Open title hopes alive and again illustrated the 19-year-old's ability to find a way to win when after Kostyuk levelled the match at a set apiece.

Prior to facing Kostyuk, reigning US Open champion Gauff had only registered four hours and 48 minutes in match time at Melbourne Park and had not dropped a set.

In contrast, her Ukrainian opponent had almost doubled that amount of court time on her way to making her first quarterfinal at a major.

Fatigue and a temperature in the low 30s may have played a factor in the 37th-ranked Kostyuk's demise after her serve was broken three times by Gauff in the final set.

She did break Gauff when the American was serving for the match at 5-0, but it proved to be a brief reprieve.

Kostyuk had forced a third set after valiantly fighting back in the second when world number four Gauff served for the match.

Gauff had broken for a 5-3 lead but she failed to hold serve, with Kostyuk winning three of the next four games to force a tiebreak.

She burst out to a 4-0 lead in the 'breaker and had four set points at 6-2, before converting on the second to level the match. 

In the early stages of the first set, it appeared Kostyuk was the one under most pressure.

She faced a break point in the opening game and was twice taken to deuce when serving in the third, but both times held her serve.

The turning point came in the fourth game when Gauff was broken for the first time. A double fault handed Kostyuk a break point, which she converted when Gauff sent a backhand return into the net.

The former world number one was broken a second time in the sixth game as Kostyuk established a commanding 5-1 lead, but Gauff was given a sniff of fighting her way back into the first set when she broke back in the next game.

She saved a set point when trailing 2-5 before holding, albeit nervously, and games were back on serve when Kostyuk was broken for a second time.

In her next service game, Kostyuk doubled faulted to give up a third consecutive break and trail 5-6 but there was yet another twist as the first set hit the one-hour mark.

Gauff posted her fourth double fault at that stage of the match as she faced a third break point, leaving the set to be decided by a tiebreak.

Kostyuk trailed 2-4 in the tiebreak but rebounded to have a set point at 6-5. She failed to convert, with Gauff winning three straight points to claim the first set.