Alcaraz, who was on a 14-match winning streak, managed to fight his way back into the contest after dropping the first set 6-3, going on to win the second set 6-4.

But Paul fought hard and dominated the net, winning 21 of a possible 23 points there, taking out the last set 6-3 to send him to the semi-finals.

"I played a really good match today," Paul told the ATP website post-match.

"You can't start any points on your heels against him or he'll take advantage of that.

"So you really have to go after your shots early in the rally and I was feeling really good on the first-strike tennis. That was the difference today."

In another upset, Alex De Minaur beat world number three Daniil Medvedev in straight sets.

A tough contest saw the Australian emerge victorious after two hours and two minutes with a 7-6 (7) 7-5 win.

De Minaur came back from 2-5 down in the first set to claim the opener in a tie-break and then came from a break down twice in the second to seal the match.

"I had to play some of my best tennis today, it has been a great week for me so far," he said after the match.

"I played the right way today. I think having played him at the end of last year gave me the confidence that I had a chance. I just had to play the right way and I am extremely proud of the effort and to still be alive."

Victory ensured De Minaur reached a first-ever Masters 1000 semi-final, where he will now face Alejandro Davidovich Fokina in the final four on Saturday.

Davidovich Fokina reached the semi-finals after beating Mackenzie McDonald 6-4 6-2.

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