Tiafoe's compelling back story and sensational run in New York, including his fourth-round upset of 23-time Grand Slam champion Rafa Nadal, made him the talk of the tournament.
"I gave everything I had these past two weeks," he told a supportive sold-out crowd at Arthur Ashe Stadium.
"I came here wanting to win a US Open and I feel like I let you guys down. This one really, really hurts. Too good from Carlos.
"I am going to come back and I will win this thing one day."
Despite the disappointment, Tiafoe said he will walk away from Flushing Meadows with a new sense of confidence.
"I proved that I can play with the best and I'm capable of winning Grand Slams," he told reporters.
Tiafoe has carried the weight of enormous expectations throughout his career, winning his sole ATP title in Delray in early 2018 before stunning the Australian Open field to reach the quarter-finals roughly a year later.
He then struggled for a while but bounced back to reach the US Open fourth round in 2020 and made his deepest run at a Grand Slam yet this year.
"Through my career I've been pretty sporadic. Playing well, veering off for a while," he said.
"I've always backed myself against the best players in the world. I'm doing it on a consistent basis, starting to beat guys more readily.
"Ready to take the next step."
Becoming the student of the game that he was in his youth when he and his twin brother lived part-time at a tennis centre in Maryland where their father worked as an on-site caretaker has also paid off.
"I'm definitely falling in love with the process and doing the work much more. I'm working smarter," he said.
He is also coping with his newfound celebrity after he came within two wins of breaking a 19-year Grand Slam drought by a US male player. He is also the first Black American man to reach the semi-finals at Flushing Meadows since Arthur Ashe in 1972.
Former first lady Michelle Obama was among those backing Tiafoe from the packed stands of the stadium named after the late Hall of Famer on Friday night.
When he first noticed her he was so stunned that he shanked a service return.
"Seeing her there was crazy ... we all know what she means," he said, adding that he met with her afterwards.
"I've seen her before, but it's a little bit different circumstance. She sees me and she's actually excited to see me. Unbelievable night."
The year's final major served as an enticing preview of the future of the sport, with fresh faces like Tiafoe, Alcaraz and Italy's Jannik Sinner ready to step out of the shadow of the Big Three.
"Obviously I would have loved to win tonight," Tiafoe said.
"But I think tennis won tonight."
