Alcaraz also rose up the rankings to occupy the coveted World No. 1 spot in men's tennis by virtue of the historic win against the Norwegian, who played his second Grand Slam final this season.
American rock star Jon Bon Jovi was in the stands to watch Alcaraz become the youngest player-ever to become World No. 1 as were stand-up comedian Jerry Seinfeld and fashion designer Ralph Lauren.
From the world of sport, American basketball star Devin Booker was at Arthur Ashe Stadium alongside model Kendall Jenner and so was DJ and songwriter Diplo.
Model Christie Brinkley, actor Lin-Manuel Miranda of Hamilton fame and Scrubs star Zach Bruff also lent star power to the evening as the Norwegian-Spanish duo played out a classic on the court.
Radio and TV host Andy Cohen, Academy-Award winning actress Anne Hathaway, actors Angus Cloud and James Marsden, and former American tennis professional Stan Smith too were present to witness history unfold at the US Open.
Also spotted in the stands were movie director Spike Lee and American musician Questlove.
Carlos Alcaraz creates history at US Open
Carlos Alcaraz rose to the occasion to become the youngest Grand Slam champion since Rafael Nadal, who won the French Open back in 2005. The Spaniard, who won three successive five-setters en route to the final, seemed to lose his way in the second set with a stream of unforced errors after prevailing in the first.
Ruud's strong serve and ability to outmanuever Alcaraz at the net had the teenager's team looking a bit worried, especially in the third set, but the Norwegian's inability to drive home the advantage proved to be a turning point.
The 19-year-old came into his own in the fourth set, much to the delight of his fans who savored the moment. With the victory, the Spaniard became only the second teenager to win the title in New York, following in the footsteps of the legendary Pete Sampras.
Despite the disappointment of losing yet another Grand Slam final, Casper Ruud made an ascent to become World No. 2 in the new ATP rankings that will be released on Monday. The 23-year-old previously lost to Rafael Nadal in the final of the French Open earlier this year