She never doubted herself, and made believers of them all. With nerves of steel and a tennis acumen that belies her 21 years, Sofia Kenin battled back to beat Garbine Muguruza 4-6 6-2 6-2 and claim the Australian Open title on her debut appearance in a Grand Slam final.

“My dream officially came true,” Kenin said before accepting the Daphne Ackhurst Trophy from fellow American Lindsay Davenport. “I am so emotional. I have worked so hard. These have been the best two weeks of my life.”

It was a fitting, fantastic finale to cap a two-week odyssey for Kenin, whose route to the title saw her run into players destined to grab the headlines in her stead. In the fourth round she beat compatriot Coco Gauff, the 15-year-old phenom who had ended the run of defending champion Naomi Osaka; in the quarter-finals she ended the inspiring, inspired run of Ons Jabeur, who went further than any Tunisian and any Arab women at a major at Melbourne Park; and in the semis she downed world No.1 Ashleigh Barty, ending hopes of a first Australian winner since Chris O’Neil in 1978.

The final, however, was all about Kenin. It was a tale of two comebacks in the match with Muguruza, one encapsulating the wider impact of the other to spark the first victory from a set down in a women’s singles final at Melbourne Park since Victoria Azarenka beat Li Na in 2013.

At 2-2 in the third set she trailed the two-time former Grand Slam champion 0-40 on her serve. The Spaniard had dictated in the opening set behind the assured net game that had carried her to the final, with Kenin flitting between errors and short balls that begged to be hit.

Kenin had found her range in the second set and began going for her shots to surge back into the match, only to be staring down the barrel of a vital break in the decider. She didn’t flinch: three nerveless down-the-line drives fended off the danger before a cross-court pass, her fifth winner in succession, sealed the critical hold.

“I knew I had to take my chance,” Kenin said. “I had to be brave by playing a two-time Grand Slam champion. All respect to her. She played a really tough match. Every point, it was such a battle. A lot of moving, a lot of emotions on court from both sides. I knew I needed to come up with the five best shots of my life.”

The fightback proved to be a crushing blow for Muguruza, who failed to win another game as her faltering serve crumbled late on. A double fault on Kenin’s second championship point – her eighth of the match – sealed the Spaniard’s fate. Despite the myriad positives to be taken from a tournament she entered unseeded and recovering from a virus, this will be a tough loss to absorb.

“The way she handled the breakpoints and the game points, these kind of moments, I think she came out doing winners, which is a tough moment,” Muguruza said. “I think she played very well. It's her first Grand Slam final for her and she performed really well.”

Only in victory did Kenin seem struck by disbelief. Uttering ‘Oh my god’ over and over as she waved to the fans and celebrated with her father and team, her acceptance speech was a flurry of thank you’s, not least to her mother back home in the United States, her parents having returned to Russia from their adopted home shortly before she was born for help raising her, before heading back to USA a matter of months later.

“I called her right after the match just to tell her that everything's fine, I won, she can just relax now,” Kenin said. “She's been really stressed at home, very superstitious. Yeah, she's just really happy. I told her I'm not going to be able to talk to you for hours, but at least you know that I won. I'm coming home, you can give me the biggest hug of your life.”

Of the 12 Grand Slam singles champions crowned over the course of the last 18 majors, Kenin is the 11^th first-time winner and fourth to clinch a title aged 21 or younger, along with Jelena Ostapenko and Naomi Osaka – whose breakthroughs came at age 20 in Paris and New York respectively – and Bianca Andreescu, crowned US Open champion last year aged 19.

Like fellow reigning Grand Slam champions Barty and Simona Halep, edged out by Muguruza in the semi-finals, Kenin is far from the tallest player on tour, a study in contrast with the rangey Muguruza. But her game is built on energy, intensity and tactical problem-solving, all twinned with assured, clean ball-striking. Of her 23 unforced errors over the course of the 123-minute contest, 15 came in the opening set.

“I feel like mental toughness has been a huge part,” Kenin said. “I've worked on that over the course of the years. Yeah, it's just paying off.

“I've played on big stadiums. I feel like that helped me to get to where I am right now. I love the big stages. That's where I'm playing. I'm playing to play on that great stage, have this amazing atmosphere. It was such an exciting atmosphere. Everyone was just cheering. It's just such an honour. They make it so much fun for me to play. It gives me hype and more motivation to keep going forward.

“I've made so many fans,” she added with a smile. “Thank you to them so much for coming and supporting me these past two weeks. It's been an incredible journey for me.”

Saturday's action on Rod Laver Arena ended with the mixed doubles final, where Nikola Mektic and Barbora Krejcikova downed Jamie Murray and Bethanie Mattek-Sands 5-7 6-4 [10-1].