Koepka, a four-time major winner, had four birdies in the match for charity, while DeChambeau didn't have any.
"Not going to lie, I just wanted to spank you," Koepka told DeChambeau, shortly before winning the match.
The result was a bit surprising, as Koepka hadn't played particularly well since helping the U.S. team win the Ryder Cup at Whistling Straits in September. He battled knee and wrist injuries this past season, then missed the cut in each of his last two starts and fell to No. 16 in the Official World Golf Ranking.
DeChambeau hasn't made a start on tour since the Ryder Cup, and spent much of his time preparing for a long-driving contest.
"I haven't played in two months," DeChambeau told TNT. "No excuses, though. I should have done better."
Koepka had birdies on Holes 2, 5, 6 and 8 to go 4 up with four holes to play. DeChambeau conceded the match after missing a birdie putt on the ninth hole. It was the fifth version of "The Match," a made-for-TV series that began with Tiger Woods and Phil Mickelson playing winner-take-all against each other. It eventually expanded to include NFL quarterbacks Peyton Manning and Tom Brady, NBA star Steph Curry and basketball Hall of Famer Charles Barkley.
The DeChambeau-Koepka matchup was one of the more highly anticipated ones because of the golfers' supposed dislike for each other. Their feud escalated at May's PGA Championship, when a leaked video showed Koepka rolling his eyes after DeChambeau walked past him while talking and interrupted an interview.
"Obviously, watching him up close and personal is pretty neat, pretty special to watch him hit the ball," Koepka said. "Like I said, there is respect there, but at the same time it was fun to come out here and settle this."
"Did we just become best friends?" reporter Amanda Balionis asked afterward.
"No," Koepka said.
On the tee box of the ninth hole, DeChambeau seemed frustrated with how well Koepka was playing against him.
"Where is this on the PGA Tour, man?" DeChambeau asked Koepka. "[You're playing] so good right now."
"It's kind of like my major right now, right?" Koepka said.
"I guess it is," DeChambeau said.
Brian Anderson, who was doing play-by-play of the match on TNT, asked Koepka if he wanted to play with DeChambeau more.
"Nah, I'm good," Koepka said.