The American, who reached his first Grand Slam semi-final at the US Open in September, flexed the same muscles that have carried him into the top 20 in the world to reach his second title-decider of the season despite a poor second set.
"It was a weird match, but happy to get through," Tiafoe said. "In these kind of matches...it's not always gonna be pretty, it's not always gonna be your best stuff, but a win is what matters."
Kwon looked nervous at times in the opener and struggled to handle Tiafoe's deft mix of accuracy, touch and power as the American rattled off five games in a row before sealing the set 6-2.
In the second set, it was Tiafoe's turn to stumble and Kwon seized on his second serve with a series of blistering returns, handing his opponent a bagel to level up the contest and send it into a decider.
Tiafoe upped the ante in the third set, winning the two break points he needed to serve for the match at 5-2, only to stumble once more.
The American sealed the win at the second time of asking, setting up a date with compatriot Taylor Fritz with a cross-court forehand winner.
Third-seeded Fritz also had to fight for his semi-final win, against Canadian Denis Shapovalov, 6-3, 6-7 (5/7), 6-3.
Going into the final "feels amazing", said Fritz, just days after he emerged from a week of hotel quarantine in Seoul where he came down with Covid-19 and had to pull out of the Korea Open.
"It's pretty crazy what I've been able to accomplish this week, just from thinking that I might not even be able to play this tournament," said the 24-year-old.
Fritz said he and Tiafoe were "really close friends, but we're also rivals".
"It'll be fun, there's always tension when we play, it's going to be a good match," he added.
Tiafoe said the pair's friendship had become closer at the Laver Cup in London, where both were in the Rest of the World Team that beat Europe for the first time in the competition's history.
"I love that guy," Tiafoe said.
"He's a great competitor, he serves well, he has a huge forehand, and he's confident and getting better too... may the best man win."
