Finau's challenge slowed down after the first seven holes and then completely broke down after a double bogey on 14th on the back nine.
Yet Finau, whose only career PGA title came in March 2016 in Puerto Rico, finished second for the fourth time this season.
Rahm, who had won three titles in his first full season in 2017, added three more in 2018.
Of the six titles, three are on PGA Tour, two on European and now the unofficial PGA Tour win at Hero World Challenge.
It just wasn't Tiger Woods' day or week as he shot 73, his second over par round of the week and finished 17th in the 18-man field.
He was four-over through front nine, before holing four birdies in five holes from 11th to 16th but again dropped a shot at 17th.
Clearly, Rahm was pleased with his progress in the first two years of his career.
Asked if he fulfilled his expectations, Rahm shot back with a smile, "How many times have there been pros that played the first two years as PGA TOUR, European Tour members to win six times?
"I just want to know. Ask Tiger how many. I love studying the history of golf and I did not expect to be here. I'm extremely pleased."
Summing up his year, Rahm said, "As I said, this year was not so much about golf, it was about me as a person, so to win as many times as I did last year, it just shows that when I get into contention, to me nothing else matters.
"Last year I think I had 14 top 10s last year, maybe more. I didn't play quite as good as last year, but I was still really good. If I can keep winning three times every year, yeah, I'll be extremely happy."
Stenson couldn't get his game going, missed a lot of putts, while Finau had a fatal double bogey on Par-4 14th, where Rahm had a bogey and that three-shot swing saw the lead become five and the battle was more or less over.
Finau admitted the double at 14th proved to be decisive.
"Yeah, in hindsight. I made a six there, one bad swing can do that on any hole and that's what happened.
"Hats off to John this week, he played incredible golf and he deserved to win this week."
Rose (65), needing to at least have a share in a three-way tie for second to regain his World No. 1 status, did get to second at 15-under and he had an eagle, too, to help him.
But then on the 18th, Finau, also at 15-under holed a 10-footer birdie to card 69 to deny Rose that.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)