Scheffler had to make an eight-foot par in near darkness on Sunday night to force the playoff.
They returned for one hole, which did not lack for drama or atmosphere. Both found the middle of the fairway on the par-4 18th. Scheffler hit his approach to 4 feet as some 3,000 fans surrounding the green erupted in cheers.
Hovland responded, just as he did on the back nine on Sunday when he made up a two-shot deficit, hitting his approach to six feet. His birdie putt downhill with a sharp left-to-right break barely caught the inside right of the cup.
Scheffler played his outside the left edge, with a little too much impact and it rolled over the left edge.
Hovland won for the 10th time worldwide, and eighth on the PGA Tour. His last victory was in the Valspar Championship in March 2025.
Hovland said: "Especially after Scottie hits it so close there, I knew I had to bring in my best to have a chance to beat him. He has certainly brought it out of me and couldn't be happier."
For Scheffler, it was his fourth runner-up finish this year after opening his season with a victory at The American Express in the California desert.
"That's a bit disappointing, especially with the putts I made (Sunday) night to stay in the tournament," Scheffler said.
There was lively banter for the playoff. A group of Norwegian fans, who had been in Boston for the World Cup, wore their soccer jerseys and chanted, "Hov-land!" as he approached his golf ball in the fairway.
The Americans began the "Scot-tie Scheff-ler!" chants to drown them out.
There was partisan cheering a year ago during a Ryder Cup where US captain Keegan Bradley rallied on the final hole to beat Tommy Fleetwood of England.
Norway's next World Cup match is in Dallas, the hometown of Scheffler.
