The contest at Sentosa Golf Club looked set to extend to a second play-off hole, but Lee was left stunned after failing to convert his short par putt on the 18th, handing DeChambeau his fourth LIV Golf victory.
DeChambeau started the final round one shot off the pace but surged into the lead at the end of the round with Lee after carding a final-round five-under-par 66, highlighted by four birdies, an eagle and a bogey.
After finishing the first play-off hole with a par, the American two-time US Open champion was prepared to head back to the tee box until Lee's astonishing miss.
"It was a bit of a shock. I thought he was just going to knock it in and I have a chance to play great golf on that second play-off hole," said the 32-year-old.
"You never want to win that way. I'll be the first to admit it.
"But golf is a fickle game. Sometimes that’s just the way the cards fall.
"I'm grateful I'm on the positive end of it. I just didn't like seeing it happen. It was tough to see that," added DeChambeau.
Despite the disappointment, Lee is hopeful of bouncing back.
"The adrenaline was pumping a little bit and I hit it a little too hard. Hopefully I can try again next week," said Lee, who was bidding to become the first wild card to win on LIV.