Alcaraz, still only 19, won nine more games than Frances Tiafoe and 29 more points, but was taken to five sets after twice losing tiebreaks.

After four hours and 19 minutes, Alcaraz emerged from the Arthur Ashe Stadium showcourt a 6-7, 6-3, 6-1, 6-7, 6-3 winner.

The United States' Tiafoe - like Alcaraz playing in a Grand Slam semi-final for the first time - saved match point in the fourth set, but ultimately could not see off the relentless Alcaraz. 

The Spaniard is just the second teenager to reach the US Open men's singles final in the open era, after American great Pete Sampras.

"You have to give everything on court," Alcaraz said afterwards. 

"Frances gave everything on court. 

"This is amazing."

Norway's Ruud awaits in the final after defeating Olympic silver medallist Karen Khachanov.

Ruud was a 7-6, 6-2, 5-7, 6-2 winner and is through to a second Grand Slam final of the year, having been the French Open runner-up.

The 23-year-old has played Alcaraz twice before and lost on both occasions - including the final of this year's Miami Masters, played on a hard court like the US Open.

Khachanov, who is Russian and was playing as a neutral in New York City with Russia's name, flag and national symbols banned over the war in Ukraine, had never reached a Grand Slam semi-final before.

In the men's doubles, Britain's Joe Salisbury and American Rajeev Ram retained their title.

They beat Briton Neal Skupski and Dutchman Wesley Koolhof 7-6, 7-5 and are the first pair since 1996 to defend the men's doubles crown.