A jittery Madison Keys got the defence of her Australian Open crown off to a stuttering start Tuesday, losing the first four games before rallying to stay in the title hunt.

The American ninth seed was a bundle of nerves on Rod Laver Arena but calmed down to clinch a 7-6 (8/6), 6-1 win over Ukraine's Oleksandra Oliynykova.

Keys stunned Aryna Sabalenka 12 months ago in a three-set epic to win her first major crown at the age of 29, but she failed to push on from there in 2025, winning no more titles.

She started her season with quarter-final exits at Brisbane and Adelaide, admitting before the Grand Slam to being nervous as defending champion.

"I've been thinking about this moment for basically a year," said Keys of walking out on centre court again. "I'm so happy to be back in Melbourne. Obviously I was very nervous at the start."

Playing at her 50th Grand Slam, in contrast to Oliynykova who was at her first, Keys sent down three double faults and was broken on her first service game.

The Ukrainian, ranked 92 and facing a player inside the top 50 for the first time, consolidated with a hold after six deuces in the second game to take charge.

Showing no nerves, she stunned the American by breaking again and raced 4-0 clear before Keys finally woke up and battled back.

She cut down on the errors and found her range on serve to win the next five games.

But Keys was broken again and it went to a tiebreak, where she slumped 4-0 behind and had to save two set points before converting for the set with a blistering crosscourt winner.

The gritty comeback was the catalyst for a far more convincing second set, as she broke straight away and raced into a 4-0 lead before sealing the match with ease after an hour and 40 minutes. (AFP)