Finau closed with three straight birdies for a 2-under 70 and kept his three-shot lead because of a late collapse by Justin Rose, who played the final two holes in five more shots than Finau required.
Reed holed an 18-footer on his final hole to take a two-shot lead as he signed for a near-perfect opening round in windy conditions at the Sheshan International Golf Club.
The Englishman, who could have returned to world No 1 with victory in Shanghai, carded a final-round 72 to end the week in third spot and four strokes behind play-off victor Xander Schauffele.
The first player of Polynesian descent to play on the PGA Tour, Finau totalled eight birdies to move to 11-under, with Reed at eight-under, along with defending champion and world number three Justin Rose and his fellow Englishman Tommy Fleetwood.
"Definitely feel like I let one get away", the Lehi resident said as he walked off the 18th green after Sunday's playoff.
Finau got a good break at Le Golf National.
American Xander Schauffele finished four strokes behind Finau after managing a one-under 71 in winds he said were "all over the place".
Finau hasn't won since the 2016 Puerto Rico Open, an opposite-field event that was held the same week as the Match Play.
First there was this lengthy birdie effort at the par-4 11th, his second hole of the day.
The birdie was enough to see Finau regain the lead and his length off the tee allowed him to take advantage of the par five last. I played really good golf.
That was a significantly better effort than Mcllroy, who was four over after two holes when he found water twice on the second on his way to a triple-bogey eight. "I know he's going to win a lot soon, obviously, because he's playing so well". "I've got to stay in attack mode, continue to make birdies and if I limit the mistakes, I think it will be a good weekend".
Reed, playing an hour ahead of the final group, drove onto the front of the 16th green for a two-putt birdie.
Dustin Johnson wouldn't figure to contribute to that opportunity. I was hitting irons where I was looking and I was able to control it, not only directional-wise, but also trajectories and what kind of heights I wanted to hit it.
The victory for Schauffele is his third in the last eighteen months, and it crescendoed. So Finau is off to another strong start, after having finished second in the Safeway Open last October to begin his '17-18 season.