'It's fun': Alcaraz steals Djokovic play at the Open

So often looking on the back foot, Alcaraz broke Paul's serve - and the world No.20's heart - when it mattered most in cruising, like only he can, into his 14th grand slam quarter-final.

Six-time grand slam champion Alcaraz had no real right to win the opening set after his start, before clinically dismantling Paul to advance to a last-eight showdown with sixth-seeded home hope Alex de Minaur or Kazakhstan's world No.10 Alexander Bublik.

Later on Sunday, world No.3 Alexander Zverev sealed his own quarter-final berth with a 6-2 6-4 6-4 win over 18th seed Francisco Cerundolo.

He will face American 25th seed Learner Tien, who thrashed three-time Open finalist and 11th seed Daniil Medvedev 6-4 6-0 6-3 to reach the last eight at a slam for the first time.

After dropping serve in the opening game of the match, Alcaraz had to work overtime to break back into the first set.

Paul had not dropped serve all tournament, holding for 38 consecutive games.

But he had not faced the world's No.1 player either.

Refusing to yield, the super Spaniard rallied back from 4-2 down, then a mini break in the tiebreaker, to snatch the set on a Paul double-fault following a 12-minute disruption to remove an ailing spectator from RLA.

While the scoreboard displayed more of a contest, Alcaraz controlled the second and third sets to prevail in two hours and 44 minutes.

"Overall it's been a really high level of tennis from both sides," Alcaraz said.

"Really happy that I got it in straight sets."

Still only 22, Alcaraz has one last chance to eclipse American Don Budge as the youngest man ever to complete a career grand slam.

The two-time Wimbledon, French and US Open champion conceded he was only too happy to tinker with his service action to complete the slam, even if it meant mimicking his great rival Djokovic.

"To be honest, I wasn't aware that it was really similar to Nole's," Alcaraz said.

"Novak's like 'Wait, that's my serve. He's gonna have to pay me some money for that serve.'

"I heard that. I have the contract over there but I haven't seen him yet.

"I just woke up and I took out my phone and had, you know, a Djokovic message.

"Like, 'All right, you have to pay me for the serve before the season'.

"Yeah, yeah, he sent me the message, so it was fun.

"I mean, these kind of things in the locker, it's fun to share with another player.

"It's especially fun when it works out and you're serving better."

De Minaur and Bublik play the feature night match on RLA on Sunday.

Tien announced himself last year when he outlasted Medvedev in five sets in a second-round match that went into the early hours,.

On Sunday, the young gun raced out of the blocks to take a commanding lead then withstood a Medvedev third-set fightback to win in straight sets in an hour and 42 minutes.

Tien, aged 20, is the youngest player to reach the quarter-finals since 2015 and the youngest American to do so since 2002.

"It feels amazing. I mean, so special to do it especially here, where it's always so special to come back and play every year," Tien said.

"This was a big goal for me this year and I'm just super-happy.

"It's (Zverev) gonna be a super-tough match

"I was able to get him the first time and then the second time we played he beat me pretty bad, actually ... it's going to be a challenge but I'm looking forward to it."

Earlier, Zverev, who is still seeking his first slam title, cruised into the last 16 with his straight-sets win over Cerundolo.

When asked if he was playing his best tennis, Zverev said: "I don't wanna jinx it so I'm gonna keep my mouth shut."