Appearing in her first Grand Slam final, 21-year-old Kenin showed relentless resolve as she battled back to beat Muguruza 4-6 6-2 6-2 on Rod Laver Arena in Melbourne.   

It capped a stunning first title for Kenin against the more experienced Muguruza, who was appearing in her fourth final at a major, and who picked up titles at the French Open in 2016 and Wimbledon in 2017.

Unseeded in Melbourne, it was Muguruza who set the early pace, breaking 14th seed Kenin in game three and threatening to run away with the first set.

Kenin dug deep to keep herself in the set, saving four break points in game seven to take the score to 4-3, with Muguruza then gifting her opponent the next game with two double-faults to get things back on serve at 4-4.

However, the parity proved brief as Muguruza broke back immediately before serving out the set.

Kenin regained her composure at the start of the second set as both players held serve with ease in the early games.

It was the American youngster who stepped things up to break in game four as she increasingly found her rhythm.

The Spaniard scrapped to stay in the set, but a resurgent Kenin broke again in game eight to take the set 6-2 and send the final into a deciding set.

Kenin fought back brilliantly from 0-40 down in game five, and then broke the Spaniard in the next set to move to 4-2 and put herself within touching distance of a maiden Grand Slam title.

The American held serve and then broke a fading Muguruza again to take the set 6-2, and with it the match and a first Grand Slam title.  

The win made the Russian-born Kenin the youngest women's Australian Open winner since Maria Sharapova lifted the trophy as a 20-year-old in 2008, and Kenin now looks destined for similar stardom.