Australian Open takeaways: Serena Williams' struggles, new Nick Kyrgios

Five things we learned from the Australian Open, the season's first grand slam, where Novak Djokovic won the men's title and Sofia Kenin was crowned women's champion:

Big Three stand firm

Every season Novak Djokovic, Rafael Nadal and Roger Federer face a stronger challenge from younger players, and every season they're able to withstand it.

Dominic Thiem pushed Djokovic all the way in Sunday's five-set final, but the Serb ultimately prevailed to join Nadal and Federer as players who have won one of the Major titles eight times.

Djokovic's victory made it 13 Grand Slams in a row won by the unshakeable trio.

Federer's resilience

You don't become one of the best players of all time by talent alone, but Federer's fighting spirit has perhaps gone unappreciated until now.

The Swiss great looked out for the count at 4-8 down in a nail-biting fifth-set super tiebreaker against John Millman in the third round, but found a way back.

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The 20-time Grand Slam champion then miraculously saved seven match points in fighting past Tennys Sandgren.

He was hampered by injury in losing in the semi-finals to Novak Djokovic, but quitting was never on the cards.

The 38-year-old has never retired in more than 1,500 matches, and he was not about to give up that proud record.

Serena may never reach 24

Serena Williams said she would be back on the practice court the day after her shock third-round defeat to China's 27th seed Wang Qiang.

The 38-year-old American also said she will not give up her pursuit of a record-equalling 24th Grand Slam title.

But her early exit raises fresh doubts that she will ever get there.

Her last Grand Slam title came in Melbourne three years ago and a growing number of younger rivals are agitating behind her.

The eventual Australian Open champion, Sofia Kenin, is just 21 and after winning her first Grand Slam title she leapfrogged Williams as America's No.1.

Littl'uns walk tall

There was a striking difference between Kenin and Garbine Muguruza when they hugged at the end of the women's final.

Two-time Grand Slam champion Muguruza stands 6ft (1.8 metres) tall, but Kenin is a comparatively short 5-foot-7.

That meant nothing on Saturday when Kenin roared back from a set down to win her maiden Grand Slam title.

Of the last four women's Grand Slam winners - Ashleigh Barty, Simona Halep, Bianca Andreescu and now Kenin - Kenin is the tallest. Barty, the World No.1, is just 5-foot-5.

“Size doesn't really matter. Just matters how tough you are and mental toughness,” said Kenin.

Kyrgios captures hearts

The 24-year-old Australian has long been derided as the enfant terrible of tennis, a hugely gifted player who seemed destined - and determined - to waste his talent.

But at his home Grand Slam he transformed perceptions and was feted as something of a hero in Australia.

It was partly because of his gutsy performances in reaching the fourth round - losing in four close sets to Rafael Nadal - but also because he spearheaded fundraising efforts for victims of Australia's deadly bushfires.

"I feel like I've made progress as a human. A tennis player - I don't really care about as much," he said.