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The top seed withstood a late charge from Italian qualifier Luca Nardi to prevail 6-1, 4-6, 6-3 and advance to the quarter-finals at the newly upgraded ATP 500 event. Trailing a set and 1-4, Nardi produced some redline tennis to stun the World No. 3, reeling off six consecutive games to force a decider. Yet in typically composed fashion, Alcaraz regrouped to seal a one-hour, 53-minute victory.

“At 4-1, 40/40 [in the second set], he played a few good points and then it seemed like he started to play like the World No. 1,” Alcaraz said. “I couldn’t do anything, I just tried to stay there, stay strong mentally. My energy levels probably went down a little bit, but credit to him. I’m really happy [that I] forgot everything and restarted in the third set.

“It was a good level mentally, I was really strong. I just tried to [let him know] that I’m there, screaming ‘Vamos’, to push me up and get the good energy again. I played really good tennis in the third set, but I’m really proud of my energy levels in that set.”

After triumphing in Beijing last October and claiming his first indoor title in Rotterdam earlier this month, Alcaraz is now on a 12-match win streak at ATP 500 events. The four-time major winner, who is making his debut in Doha, will next face Jiri Lehecka, who earlier eased past Fabian Marozsan 6-4, 6-2 in 63 minutes.

Alcaraz and Nardi, the world number 85, are no strangers. Born just three months apart in 2003, the two came through the junior ranks together and know each other’s game well. The relaxed nature of their friendship came to the fore in the fifth game of the final set, when Nardi pulled off a stunning tweener followed by a perfect drop shot to leave even Alcaraz, who offered a fist bump, in awe.

Leading a set and a break, while playing and moving freely, Alcaraz appeared to have one foot in the locker room. Yet Nardi, chasing his first ATP Tour quarter-final, produced an inspired turn in form, during which he shifted to a more aggressive approach on return and found comfort behind his serve. The Italian won 15 of the last 16 points of the second set, and also won three consecutive service games to love, to spark hopes of a stunning comeback.

It wouldn’t have been the first time that Nardi had produced a major shock on the ATP Tour. Eleven months ago in Indian Wells, the 21 year-old pulled off one of the upsets of the season by defeating the then-World No. 1 Novak Djokovic. But Alcaraz, aiming to win back-to-back titles, found another gear in the deciding set to extend his winning streak to seven matches.

In other action at the Qatari event, Matteo Berrettini secured back-to-back wins on the ATP Tour for the first time since October last year by defeating Tallon Griekspoor 7-6(4), 6-7(6), 6-4 in a serve-dominated clash. The Italian hit 50 winners, including 23 aces.

“I went on court really focused, I wasn’t feeling the ball as well as yesterday,” said Berrettini, who defeated two-time champion Novak Djokovic on Wednesday for his first-career win over the former World No. 1. “I fought really hard [across] three sets. [I made] a couple of mistakes in the second-set tie-break, but I kept fighting. I’m really proud of my mental toughness.”

Berrettini, the former World No. 6, won 89 percent (64/72) of first-serve points, during the two-hour, 27-minute clash. Neither player had faced a break point until 4-4 in the final set, when the Italian converted the only one of the match before fittingly serving it out with an ace.

In his 34th tour-level quarter-final, Berrettini will face Jack Draper. The eighth seed defeated qualifier Christopher O’Connell 6-2, 6-1 to reach his sixth consecutive quarter-final at ATP 500 tournaments, which includes his first title at this level in Vienna last October.