Former world No.1 Muguruza won the opening set but was eventually overhauled by red-hot American sensation Kenin 4-6 6-2 6-2 in Melbourne on Saturday.

Unseeded for the year's opening Major after a tough run of form, Muguruza has looked like a player reborn since reuniting with former coach Conchita Martinez after the pair split two years ago.

But featuring in her first Major final since winning Wimbledon in 2017, Spanish star Muguruza fell short on Rod Laver Arena.

Asked if she felt like she was back, Muguruza responded: "Back? Hmm, OK. If people see it because I'm in a grand slam final, that makes sense.

"But I feel like I was playing a lot of tournaments. I was on the tour, guys. I didn't disappear. I was there. Not reaching final rounds, for sure."

After No/14 seed Kenin levelled the match, Muguruza had a golden opportunity to break first in the third set.

The two-time Major champion earned three break points at love-40 in the fifth game, however, Kenin hit four groundstroke winners and an ace to hold before eventually breaking herself and powering to a first slam success.

"I'm not very happy about my performance," Muguruza said. "I think I had to play better today because she came up with a great level. 

"I think at the important moments I didn't find my shots. I think she found her shots, I didn't find my shots. I did fail a little bit lack of energy after so many matches. Physically it was a tough battle out there. 

"It's just a tough moment. Right now it's tough to be happy, although it has been an incredible tournament. You lose a final, but you got to make it to the final to be able to win or lose. I think she played very well."