Tiafoe won their semifinal 6-3, 7-6 (11) after saving six set points in the tiebreak. He seized his chance at 11-10 down to win the next three points, sealing victory with a stinging return shot.
"Crazy match, crazy second set, I'm just happy to get through," he said. "I wasn't relaxed in that tiebreak at all."
Tiafoe has a 2-4 win-loss record in finals. He won his last final in April on Houston clay against Tomás Martín Etcheverry.
Hungarian player Fucsovics came through qualifying in Stuttgart and upset Tiafoe's friend and fellow American player, Taylor Fritz, in the quarterfinals on Friday. He was bidding to reach his first final since 2021 but his return game was notably lacking against Tiafoe as he failed to force a single break point.
Struff dropped a set for the first time in the tournament but still made his third career final by upsetting the fourth-seeded Hurkacz, a former Wimbledon semifinalist.
Struff is 0-2 in finals and looking for his first career title on Sunday. He said it "means a lot" to have his family in the crowd because his first final in Germany in Munich in 2021 was played without a crowd amid the coronavirus pandemic.