Rafael Nadal continued his pursuit of a record-breaking 21st major title by beating Karen Khachanov in four sets to reach the Australian Open fourth round.

The Spanish sixth seed faces France's Adrian Mannarino in the last 16.

Mannarino came through a mammoth four-set match against Russia's 18th seed Aslan Karatsev that lasted four hours and 48 minutes.

The pair were last on after a busy day on Margaret Court Arena, with the 33-year-old eventually completing a 7-6 (7-4) 6-7 (4-7) 7-5 6-4 victory at 2.33am local time.

German third seed Alexander Zverev and Italian seventh seed Matteo Berrettini both also reached the fourth round.

Berrettini overcame Spanish prospect Carlos Alcaraz in an enthralling five-set battle, after the Spanish 18-year-old - the youngest man in the draw - fought back from two sets down.

Berrettini held his nerve to win the deciding tie-break 6-2 7-6 (7-3) 4-6 2-6 7-6 (10-5) on the Rod Laver Arena.

Zverev had a more straightforward passage into the last 16, seeing off Moldovan qualifier Radu Albot 6-3 6-4 6-4.

Nadal sensing big opportunity

The 35-year-old, is the only former Melbourne champion remaining in the men's draw - although his sole Australian Open title came 13 years ago.

With the absence of fellow 20-time Grand Slam winners Novak Djokovic, deported over his vaccine status after having his visa revoked, and Switzerland's Federer, who is recovering from injury, this tournament offers Nadal a major opportunity.

Having won the Melbourne Summer Set in the build-up to the tournament, he has made a flying start on his Grand Slam return following a five-month lay-off because of a foot injury and is yet to drop a set after three matches.

Nadal, who described it as "my best match since I came back", raced 3-0 ahead and dropped only one point on his serve in a devastating opening set.

He carried that momentum into the second set, breaking Khachanov in the opening game. It was not all plain sailing - the Russian creating a break opportunity when trailing 2-1 - but the imperious Nadal responded by winning three consecutive games.

Khachanov battled on admirably, however, and saved a break point early in the third set before breaking Nadal for the first time, from 40-0 down, for a 3-1 lead.

The Russian survived three break points in the following game and although he was unable to clinch three of his own when 4-1 up, it did not prove costly as he forced a fourth set.

The set-back brought a determined reaction from Nadal, who sealed a double break with a ferocious cross-court forehand before serving out the match.

'Alcaraz is unbelievable'

Wimbledon finalist Berrettini looked in control for the first set and most of the second before Alcaraz grew in confidence, breaking back and taking it to a tie-break that he lost.

But the young Spaniard clinched the third set before storming through the fourth to set up a decisive finale.

Berrettini turned his ankle early in the set and needed treatment, but the 25-year-old Italian dug in to fend off a break point and then brought up match point at 6-5.

Alcaraz, who beat Berrettini at the Erste Bank Open in Austria last year, saved the point with a fizzing second serve and battled back to hold and force the tie-break.

However, it was the more experienced Berrettini who edged ahead and did not let up in the first-to-10 decider, winning a match that lasted more than four hours.

"He is unbelievable," said Berrettini of his teenage opponent. "He is impressive and will only improve playing matches like this, he has shown everyone his potential. Luckily today I won."

Berrettini's next opponent is Spanish 19th seed Pablo Carreno Busta, who defeated another rising star, American Sebastian Korda, 6-4 7-5 6-7 (6-8) 6-3.

Zverev will meet Canadian 14th seed Denis Shapovalov, who beat American Reilly Opelka 7-6 (7-4) 4-6 6-3 6-4.

Meanwhile, French 17th seed Gael Monfils overcame Chile's 16th seed Cristian Garin 7-6 (7-4) 6-1 6-3.

He will play Serb Miomir Kecmanovic, who knocked out Italian 25th seed Lorenzo Sonego 6-4 6-7 (8-10) 6-2 7-5.