Carlos Alcaraz is one step closer to tennis history…

The 19-year-old Spanish professional tennis player defeated 2014 US Open champion Marin Cilic in the fourth round of the grand slam tournament, as he continues his march towards becoming the youngest World No. 1 in ATP Rankings history.

Alcaraz, the third seed at the US Open, outlasted the former World No. 3 6-4, 3-6, 6-4, 4-6, 6-3 to reach the quarterfinals at Flushing Meadows for the second consecutive year.

“Honestly, I have no idea,” Alcaraz said of how he won the match. “It was pretty, pretty tough at the beginning of the fifth set [being a] break down. But Marin was playing unbelievable. I believe in myself all the time. Of course the support today in Arthur Ashe [Stadium] was crazy. Without you guys, it wouldn’t be possible to win this match tonight, so thank you very much for the support tonight, thank you.

“I would say 100 per cent of the energy I put in the fifth set was thanks to you. It was unbelievable.”

For a moment, Alcaraz’s tournament hopes of reaching No. 1 on 12 September were slipping away. Cilic caught fire from the baseline and powered his way back into the match to force a decider and led by a break early in the fifth set. But Alcaraz showed his competitive spirit and immediately struck back before surging to the finish after three hours and 53 minutes.

“After a fourth set [when] I had a lot of opportunities… it was tough for me to come back in the fifth set, to stay strong mentally,” Alcaraz said. “But as I said, the energy that I received today made me win.”

With Daniil Medvedev and Rafael Nadal losing over the past two days, the stakes have been raised for Alcaraz in New York. Not only is the teen pursuing his maiden Grand Slam title — he is also trying to ascend to the pinnacle of men’s tennis.

If the Spaniard reaches the final and Casper Ruud does not, Alcaraz will climb to World No. 1 on the Monday after the US Open. If Ruud makes the final and Alcaraz does not, the Norwegian will ascend to the top spot. If both men make the championship match, the winner will depart with the trophy and World No. 1. Alcaraz is up to No. 2 in the ATP Live Rankings.

Alcaraz was focused on the player in front of him in the fourth round, Cilic, and he needed to be. The Spaniard withstood a barrage of booming groundstrokes from the Croatian in the early hours of the morning and found some of his best tennis when it mattered most. Alcaraz dropped to his knees to celebrate his victory and both players shared special moments with the remaining crowd inside Arthur Ashe Stadium, thanking the fans on their way off the court.

Early in the fourth set, the dynamics of the match changed when Alcaraz began to return Cilic’s serve from near the back wall, allowing the 33-year-old to take the first big strike in rallies. Alcaraz was left scrambling to avoid playing defence against his aggressive opponent.

When Alcaraz missed a forehand to go down a break in the fifth set, Cilic appeared in control. The Croatian has plenty of experience in difficult moments and was the only Grand Slam champion remaining in the draw.

But Alcaraz’s resolve never waned. The third seed continued battling and that paid dividends when he found an incredible angle to get back on serve. He never looked back from there, finding a way through the clash in which he struck 28 winners and converted six of his 18 break points.

Next up for the Spaniard will be 11th seed Jannik Sinner, another former Next Gen ATP Finals champion. The Italian also needed five sets to win his fourth-round match.

“I played a couple of times against him. He’s a great player, a really, really tough one,” said Alcaraz, who trails their ATP Head2Head series 1-2. “I lost twice in the past two months, so I will have to be ready for this battle against Jannik.”