The American world number 65 dominated the match on Rod Laver Arena at Melbourne Park, taking the first set 6-4.

He built a 5-3 lead in the second, when top seed Nadal took a medical timeout.

The Spaniard clinched a famous victory at last year's Australian Open - his first triumph at the tournament since 2009 - and a 14th French Open title to give him a record 22 career Grand Slams in men's singles tennis.

The now-36-year-old said he had been experiencing issues with his left hip for a "couple of days" prior to his second round match, but was adamant he "didn't want to retire, to be the defending champion here".

McDonald went on to win the second set 6-4 and the third 7-5, and Nadal congratulated his opponent but admitted he was "destroyed mentally at this time" following his latest injury, and hopes it will not "put me out of the court for a long time".

Japan's Yoshihito Nishioka awaits McDonald in the third round after his comfortable 6-3, 6-4, 6-2 victory against the Czech Republic's Dalibor Svrčina.

Russian Daniil Medvedev, competing as a neutral due to measures imposed in response to the war in Ukraine, was a beaten finalist at the last two Australian Opens.

He continued his bid for a second Grand Slam with a routine 7-5, 6-2, 6-2 win against Australian wildcard John Millman on Margaret Court Arena.

American Sebastian Korda is set to be his third-round opponent after a 6-2, 7-5, 6-4 triumph over Japan's Yosuke Watanuki.

The third seed Stefanos Tsitsipas of Greece, a three-time semi-finalist in Melbourne, eased past another home favourite in Rinky Hijikata 6-3, 6-0, 6-2, and is set to face Tallon Griekspoor next following his 6-4, 6-4, 6-4 victory against Botic van de Zandschulp in an all-Dutch clash.

Sixth seed Félix Auger-Aliassime of Canada survived a scare against Slovakian Alex Molčan on Margaret Court Arena, coming from two sets down to win 3-6, 3-6, 6-3, 6-2, 6-2, 6-2.

Argentina's Francisco Cerúndolo is set to play Auger-Aliassime in the next round after beating France's Corentin Moutet 3-6, 6-4, 6-2, 7-5.

Tenth seed Hubert Hurkacz of Poland was also involved in a five-set match, but held his nerve to set up a third round tie against Canadian Denis Shapovalov.

Hurkacz prevailed 3-6, 7-6, 2-6, 6-3, 6-3, while Shapovalov beat Japan's Taro Daniel 6-3, 7-6, 7-5 on the 1573 Arena.

In the women's singles, top seed and tournament favourite Iga Świątek of Poland had a trouble-free passage to the third round, seeing off Colombia's Camila Osorio 6-2, 6-3 on Rod Laver Arena.

Spain's Cristina Bucșa is her next opponent after she came from behind to beat Canada's Bianca Andreescu 2-6, 7-6, 6-4.

Last year's runner-up Danielle Collins of the United States is set to play Kazakhstan's Wimbledon champion Elena Rybakina in the third round after both players won their matches today.

Collins won a third-set tiebreak 10-6 to beat Czech Republic's Karolína Muchová 6-7, 6-2, 7-6 on Margaret Court Arena, while Rybakina proved too strong for Slovenia's Kaja Juvan in a 6-2, 6-1 success on John Cain Arena.

Third seed Jessica Pegula of the US is into the third round with a 6-2, 7-6 win over Belarusian neutral Aliaksandra Sasnovich on Rod Laver Arena.

Ukraine's Marta Kostyuk, who has declared she would not shake hands with players from Russia or Belarus, is her next opponent following a 6-2, 6-1 victory against Olivia Gadecki of Australia on Kia Arena.

Sixth seed Maria Sakkari of Greece came from behind against Russian neutral Diana Shnaider to triumph 3-6, 7-5, 6-3 on Margaret Court Arena, and is set to take on China's Zhu Lin in the third round after her 6-2, 6-2 success against Switzerland's Jil Teichmann.

Coco Gauff of the US, seeded seventh progressed to a third round tie against compatriot Bernarda Pera after a 6-3, 7-6 victory over Britain's former US Open champion Emma Raducanu on Rod Laver Arena.

Pera was a 6-4, 6-4 winner against China's Zheng Qinwen.

Two-time winner Victoria Azarenka of Belarus, competing as a neutral, chalked up her 150th Grand Slam match win by thrashing Argentina's Nadia Podoroska 6-1, 6-0 on Kia Arena, and 10th seed Madison Keys of the US is set to be her third round opponent after a 6-3, 6-2 victory over China's Wang Xinyu on Margaret Court Arena.

The 15th seed Petra Kvitová of Czech Republic, a finalist in 2019, was a high-profile player to exit at the second-round stage as she lost 7-5, 6-4 to Ukraine's Anhelina Kalinina on John Cain Arena.

Weather-related delays meant some first round ties were still outstanding, with eighth seed Daria Kasatkina the highest-ranked player to exit so far after losing 6-1, 6-1 to Russian compatriot Varvara Gracheva.

Both players were competing as neutrals.

Rain caused further disruption, forcing a six-hour delay to play on outside courts which led to several matches finishing late in the evening.

Further second round matches in the men's and women's singles are scheduled to be held tomorrow.