He started the final round three shots behind leader Davis Riley, whose rough start opened opportunities for the field.
“The start got the best of me and kind of put me behind the eight-ball early unfortunately,” Riley said.
Thorbjornsen took advantage, surging into the lead at No. 14 with his third of four birdies in a six-hole stretch and closing with a clutch, curling putt that went in the right side of the cup.
He’s the eighth first-time winner this season on the PGA Tour and the second straight, following Jackson Koivun’s victory last week at the 3M Open.
“It was such a battle, playing with some great players,” Thorbjornsen said. “Everyone was in the mix after nine holes.”
Xander Schauffele (65) briefly led during the final round and finished second, two shots behind Thorbjornsen, one of his playing partners Sunday.
“I played really well and he just beat me straight up, so hats off to him,” Schauffele said.
Riley (70) was another stroke behind in third, falling out of the lead with four bogeys.
Rasmus Hojgaard (68) was alone in fourth, four shots back.
Hideki Matsuyama (64), Matt Wallace (67), and Kristoffer Ventura (68) were another stroke back, tied for fifth.
Thorbjornsen was born in Cleveland; his family relocated to Massachusetts so his mom, Sandra, could work toward an MBA at Babson. He spent his first three years of high school at IMG Academy in Florida, then — with his Stanford commitment set and looming — transferred to Wellesley for his final year in 2019-20.
He won the 2018 US Junior Amateur over Akshay Bhatia, who has three PGA Tour wins, and was a runaway winner of the 2021 Massachusetts Amateur as a 19-year-old, trouncing Matt Parziale — a US Mid-Amateur champion and three-time major participant — in the final via 18 birdies in 30 holes at Brae Burn CC.
He’s played in three US Opens, making the cut in 2019 at Pebble Beach, and contending at the 2022 Travelers Championship in Connecticut as an amateur before finishing fourth. Thorbjornsen turned professional in June 2024 after earning his tour card by topping the PGA Tour University rankings. His best Tour finishes before Sunday were four top-threes, most recently a third at the Phoenix Open in February. He tied for fourth at last year’s Rocket Classic, and was coming off making the cut at the British Open last month.
Thorbjornsen chipped in from 35 feet for birdie at No. 12 on a day when he accurately aimed for pins that left him with some short birdie putts before his long one on his 72nd hole.
He had a bogey-free round, an accomplishment many other players on the leaderboard were unable to pull off on a day that started with rain and became windy when the clouds cleared.
Riley started with a one-shot lead and quickly lost it — and couldn’t find his ball in fescue at No. 4 after about a dozen people helped him try — with three bogeys through six holes.
He rallied with three birdies in a seven-hole stretch before giving back a stroke with a bogey at No. 17, taking away his chance to possibly force the tournament into a playoff.
Thorbjornsen will be unable to defend his title next year, as it was the eighth and final Rocket Classic. The PGA Tour is moving to a new model for 2028, effectively creating two tours, and Rocket Mortgage decided not to exercise its option to host another tournament next year.