MELBOURNE, Australia -- On another brutally hot day at the Australian Open, powerful Czech qualifier Denisa Allertova and Croatian comeback kid Petra Martic were the first singles competitors to advance into the fourth round of the year's first Grand Slam.

World No.130 Allertova moved into the second week of a Grand Slam for the first time in her career, as she dispatched Poland’s Magda Linette, 6-1, 6-4 on Margaret Court Arena on Friday. The hard-hitting Czech had 23 winners in the match, and continues her hot streak in Melbourne, where she has made it through three qualifying matches and three main draw matches without the loss of a set.

"It's the biggest win of my career, I've been through such a lot to get here," Allertova said to the media after the match. "Starting on Thursday, I had three rounds of qualifying then three rounds in the main draw. It's just an amazing feeling."

Martic had to work much harder for her win, but ultimately outlasted qualifier Luksika Kumkhum of Thailand, 6-3, 3-6, 7-5, in two hours and ten minutes on Rod Laver Arena. Martic, celebrating her 27th birthday today, finds herself in the fourth round at a major for the third time in the last four events, after reaching that point at the French Open and Wimbledon last year.

Kumkhum had 44 winners, compared to Martic's 18, but Martic was more consistent and craftier, and the Croat won a higher percentage of her service points than the Thai qualifier did, which was enough to eke out a win.

Read more: Petra Martic relishing 'second chance' in Paris

Allertova took the first set easily, as the qualifier used her powerful serve to completely disarm Linette in 21 minutes. The Czech clinched the set with another strong serve, followed by a punishing forehand. Each player had five unforced errors in the opening frame, but Allertova had ten winners, while Linette could only manage two.

But Linette, the World No.74, opened the second set strongly. The Polish player broke Allertova at love for 2-0 after the Czech double faulted down break point, and then held with an ace to take a 3-0 lead.

Serving at 4-2, though, Linette let a 40-0 lead slip and found herself in a battle of a game. After watching one break point slip through her fingers, Allertova hit a forehand winner down the line to claim a second chance, and powered another forehand to force an error, getting the set back on serve.

Allertova rediscovered her mojo at that point, recovering the big-hitting game which led her to the dominant first set. After holding for 4-4 with an ace, the Czech quickly broke Linette to lead 5-4, giving herself a chance to serve for the match. Allertova only needed one match point to complete a five-game winning streak and obtain a breakthrough victory.

Allertova will play World No.4 Elina Svitolina in the fourth round, after Svitolina beat her compatriot, 15-year-old qualifier Marta Kostyuk, 6-2, 6-2. "I knew [Svitolina] in juniors and have watched how she has developed and become a top player," said Allertova. "My coach will be watching her here and prepare a plan for me."

Martic and Kumkhum split the first two sets in a seesaw affair which found both players using every inch of the court within numerous grueling rallies. Those were just a prelude to the deciding set, which took over an hour before a victor was determined.

The players exchanged breaks in the first two games of the third set, as Kumkhum tried to dictate play, typically from her backhand side, while Martic deployed slices and drop shot attempts to rattle the Thai, who was making her first appearance in the third round of a major.

Kumkhum survived a 10-minute game to hold for 3-2, fending off four break points in the process, and she seemed to have the momentum in the middle of the set. The Thai reached double break point on Martic's serve at 4-3, and converting either of those would have given her the chance to serve for the set and claim a famous win.

But Martic used solid serving to escape that difficult position and hold for 4-4. It was the Croat who grasped the momentum from that point forward, holding easily for 5-5 and then taking advantage of forehand unforced errors from Kumkhum in that game. A tired-looking double fault by Kumkhum down break point gave Martic the 6-5 lead, and sealed her fate.

Kumkhum hit a scorching backhand down the line in the next game, which gave her hope, but more unforced errors from her forehand followed, bringing Martic to match point. Martic received a final birthday gift from Kumkhum as the qualifier pushed a final service return into the net, sending the Croat into the fourth round at a major once more.

"I just look back and I can't believe what season I had," Martic said in her press conference after the match, when asked about her comeback from outside of the Top 250 last year. "I'm just living my dream. When I started, I really had no idea what to expect. I didn't know how my body was going to react, whether I can actually handle so much work. But it's been going great. I'm just really so happy about it."