The third seed's winning ace sealed the victory long after midnight - at 2:50am local time at the Arthur Ashe Stadium n New York City - with the score ending 6-3, 6-7, 6-7, 7-5, 6-3.

Alcaraz had opportunities to progress in just three sets, but lost both tiebreaks to Sinner, who also squandered a match point in the fourth set.

Alcaraz managed to turn the fourth set in his favour, but was on the back foot once again in the fifth when Sinner broke.

After breaking back to make it level again, the 19-year-old Alcaraz made the most of his opponent's unforced errors to earn a pivotal second break to make it 5-3, with a chance to win with serve.

Despite Sinner's best attempts, Alcaraz signed off the match with an ace.

The match lasted five hours and 15 minutes, just 11 minutes short of the all-time US Open men's singles record dating back to 1992 when Sweden's Stefan Edberg defeated American Michael Chang.

His reward for winning the mammoth match is a semi-final contest against American Frances Tiafoe.

Tiafoe continued his fairytale run with a 7-6, 7-6, 6-4 win over ninth seed Andrey Rublev of Russia, who was playing as a neutral.

He became the first American man since Andy Roddick in 2006 to reach the last four of their home Grand Slam in singles, producing an assured performance in front of a boisterous home crowd.

The 22nd seed did not have his serve broken all match, and served 18 aces as he backed up his famous win over Spain’s Rafael Nadal, the second seed, on the same court on Monday (September 5).

Fittingly, he became the first black American to make the US Open men's singles semi-finals since the man who the stadium is named after - Arthur Ashe - did it in 1972.

In the women's singles quarter-finals, world number one Iga Świątek kept her hopes alive of winning a third Grand Slam title and a first on a hard court following a straight-sets victory over American eighth seed Jessica Pegula.

The Polish player defeated Pegula - who had made the quarter-finals of the US Open for the first time in her career - in a match which lasted nearly two hours and was marred by unforced errors.

Świątek won 6-3, 7-6 to set up a final four tie with Aryna Sabalenka.

Sabalenka, who is from Belarus but playing as a neutral at this tournament, defeated Karolína Plíšková of the Czech Republic 6-1, 7-6.

She raced through the first set against an out-of-sorts Plíšková, before a highly competitive second set with neither player facing a break point.

Sabalenka produced an impressive serving display in the tiebreak, winning five of the last seven points to beat her opponent for the third time in five meetings.

Victory means Sabalenka has reached the semi-finals of the tournament for the second year in a row.