Carlos Alcaraz says he is pleased to see the recent changes to his serve pay off, describing it as an "important weapon" during his serene run to the last eight of the Australian Open.

A straight-set win over American 19th seed Tommy Paul took world number one Alcaraz into a 14th Grand Slam quarter-final, surpassing the record previously held by Bjorn Borg and Boris Becker (13) for the most of any player in the Open era before turning 23.

After the match, Alcaraz spoke at length about the tweaks he has made to his serve in recent months - joking with the crowd on Rod Laver Arena about the similarities it now has with Novak Djokovic's serve.

"I'm surprising myself to be honest," said the six-time Grand Slam champion, who is yet to drop a set during his first four matches in Melbourne.

"The serve is something I've been working on for a long time. I'm really happy to see the improvement of the serve and to have a high percentage.

"After every set, I try to take up my percentage. I look at the screen after every set. In general, [in] the four matches I've played, the serve has been an important weapon for me."

Alcaraz was broken by Paul in the first game of the match but the 22-year-old responded to force a tie-break, which was halted for almost 15 minutes because of a medical emergency in the crowd.

The Spaniard eventually clinched it thanks to a Paul double fault, and a break of serve in each of the next two sets helped Alcaraz wrap up a 7-6 (8-6) 6-4 7-5 win in two hours and 44 minutes.

He did not face a break point in sets two and three, while he ended with a first-serve percentage of 70% - his second-best performance on that metric during his four matches of the tournament to date.

His best (71%) came in his third-round match with France's Corentin Moutet, while his lowest - a still respectable 64% - came against Germany's Yannick Hanfmann in round two.

Alcaraz, who has never been beyond the quarter-finals in Melbourne, will continue his bid to complete a career Grand Slam against Australian sixth seed Alex de Minaur, who beat Kazakhstan's Alexander Bublik 6-4 6-1 6-1 in Sunday's late session in front of a home crowd.

'Healthy' Zverev breezes into last eight

Should Alcaraz progress to the last four, a semi-final against Alexander Zverev may await.

The German third seed, who ended the hopes of Great Britain's Cameron Norrie in round three, impressed in a 6-2 6-4 6-4 victory against 18th seed Francisco Cerundolo of Argentina.

Zverev, who was beaten by Jannik Sinner in last year's Australian Open final, said he is "as healthy as he has been for the past 12 months" as he chases a maiden Grand Slam title.

In last year's majors, he followed his runner-up finish in Melbourne with a quarter-final at the French Open, a surprise first-round exit at Wimbledon and a third-round loss at the US Open.

"I had a lot of issues with my body and a lot of injuries that prevented me from playing 100%," said the 28-year-old. "I played through them but I was not really feeling great.

"When I'm healthy, I'm happy on the court and everything becomes a bit easier. I don't want to jinx it but hopefully we have three more tough matches and hopefully I can stay that way."

Zverev's next opponent will be American 25th seed Learner Tien, who overcame an early nosebleed to reach the last eight of a Grand Slam for the first time in his career.

The 20-year-old put together a run of 11 successive games in a crushing 6-4 6-0 6-3 win against former US Open champion Daniil Medvedev, who - playing in his 35th Grand Slam tournament - was on the wrong end of a 6-0 set for the first time in a major.