Sinner becomes first Italian man to reach US Open final after downing Draper
Australian Open champion Sinner came through 7-5, 7-6(3), 6-2 and will face either Taylor Fritz (26) or Frances Tiafoe (26) for the title on Sunday.
A clearly unwell Draper, the first British man in the semi-finals since Andy Murray won the title in 2012, wilted in the closing stages, having vomited on court earlier in the match.
"Jack and I know each other very well, we are great friends off court," said Sinner who unleashed 43 winners in the match where he also injured his wrist in a nasty fall.
"It was a very physical match. He's so tough to beat so I'm excited to be in the final."
In a gruelling three-hour match, Draper was eventually undone by 10 double faults and 43 unforced errors as well as his illness.
"In the final, it will be a very tough challenge whoever I play," added Sinner of being guaranteed to face an American opponent.
"I'm happy to be in that position because if you are in the final on a Sunday it means you are doing an amazing job."
World number 25 Draper arrived in his first Grand Slam semi-final having only been broken three times in five rounds and not having dropped a set.
However, Sinner started eating into that streak with a break for a 4-3 lead, quickly wiped out by the Briton.
Draper was broken again on the back of his sixth double fault in the 11th game before the Italian top seed served it out with a love game.
In a dramatic second set, Draper vomited at the side of the court before Sinner then fell chasing a Draper shot, hurting his left wrist as he attempted to break his fall.
Sinner won that point, but Draper held serve for 5-4.
Two trainers then appeared on court at the same to treat the two players' ailments, although Sinner required a full medical timeout.
It was a brief scare, however, as the Italian raced through the tiebreak to secure a two-set lead.
Draper looked physically spent and was reduced to walking pace as the third set and match slipped away from him.
