US Open: The energy I received was unbelievable, says Carlos Alcaraz after winning a historic battle

World No. 3 Carlos Alcaraz on Thursday acknowledged the energy he received from the crowd after he defeated Russia's Jannik Sinner in what turned out to be the second-longest match in the history of the US Open.

During the five-hour and 15 minutes classic encounter, Alcaraz saved one match point in the fourth set to eventually become the first teenager to reach a Grand Slam semi-final since 19-year-old Rafael Nadal did so in 2005. The senior Spaniard bagged the milestone at the Roland Garros.

The 19-year-old Alcaraz also became the youngest US Open semi-finalist since Pete Sampras in 1990.

"I feel great to be in my first semi-final in a Grand Slam. I feel better reaching a semi-final here [at the] US Open. This tournament is amazing. The crowd is amazing, I would say the best in the world. Probably at the end of the match, I was [at] my end. It was really, really tough for me.

"[But], during the whole match, five hours, 15 minutes of the match, I felt great physically. The level of tennis that we played, it was really, really high. But I felt great. The energy I received in this court at 3 a.m., it was unbelievable. I mean, probably in other tournaments, everybody [would go] to their house to rest. But they [stayed] in the court, supporting me. It was unbelievable," Alcaraz said in his post-match press conference.

With the five-set victory over Sinner, Alcaraz also qualified for the Nitto ATP Tour Finals for the first time. He also further improved his season's record to 44-9. This year, Alcaraz has already won four titles, including two ATP Masters 1000. Alcaraz, who is aiming to win his maiden Grand Slam, has won titles this year in Rio de Janerio, Barcelona, Miami, and Madrid.

US Open: It was really difficult to close the match, says Carlos Alcaraz

The match finished at 2.30 am local time and even though it was so late, Alcaraz signed autographs for fans and tossed his sneakers into the crowd.

"Honestly, I still don't know how I did it. You have to believe in yourself. I believed in my game. It was really difficult to close out the match. I tried to stay calm, but it is difficult at the moment," Alcaraz had said in his on-court interview soon after the game ended at Arthur Ashe Stadium.

Alcaraz is scheduled to next play America's local boy Frances Tiafoe in the semi-final. Tiafoe reached the last-four round after defeating Andrey Rublev and that made him the first American man to reach the US Open semi-final in 16 long years.

Speaking about his upcoming encounter with Tiafoe, Alcaraz said, "It's going to be really, really tough. Everybody knows his level of Frances. He has beaten Rafa Nadal and Rublev. He's playing unbelievably right now. High confidence. He loves the crowd. He loves this court. I'm going to have to play my best."

Alcaraz and Tiafoe will lock horns on Friday at New York's Flushing Meadows. The other semi-final is between Norway's Casper Ruud and Russia's Karen Khachanov.