Reavie had five birdies through nine holes but after he made the turn, his scorecard was colored with three consecutive bogeys.
Chasing his eighth title and second of the season, 40-year-old Kuchar leads by two shots from Andrew Putman (67) with countrymen Keith Mitchell (63) and Chez Reavie (66) a further two shots back. Five 3s in your first seven holes on the back nine with the tournament in the balance is a nice way to close a two-week stay in Hawaii.
Armed with a three-stroke advantage with just two holes remaining, Kuchar held firm and, after a cast-iron par at the penultimate hole, he completed a comprehensive win with his 24th birdie of the tournament at the 72nd hole.
"I anticipate needing another good score tomorrow", Kuchar said. "If you play well, you can make birdies", Kuchar said.
But Kuchar edged back in front when he pitched to three feet to set up a birdie at 10 before holing from 10 feet at the 12th, although Putnam then regained a share of the lead with a clutch 20-foot putt for birdie at the 13th.
He won the Mayakoba Classic in Mexico two months ago, another finish that was tighter than it needed to be.
Leader Kuchar has enjoyed a new lease of life in the early part off the 2018-19 season.
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Chelsea legend Lampard said: "We have asked, but I don't think he's leaving Chelsea ". I don't want a very important player as Cesc unhappy.
Kuchar matched the lowest 36-hole score of his PGA Tour career.
I get where he's coming from and know that he's just trying to build confidence, but I might have to amend my "Spieth will win three times in 2019" take in a few weeks.
Kuchar was sliding his way out of the top 50 toward the end of a year ago, when he failed to make a Ryder Cup or Presidents Cup team for the first time since 2009.
Kuchar is 2-2 when he has the 54-hole lead going into the final round.
"It's not often you feel like you know what you're doing with your swing and the ball's reacting the way you want it to and you're able to maneuver the ball the way you want", Kuchar told reporters. "I just couldn't keep up with him". Four players finished in a tie for third at 17-under including Australian Marc Leishman and Canadian Corey Conners.
DIVOTS: Gary Woodland, who didn't shoot worse than 68 last week and still had to settle for runner-up at Kapalua, was among 10 players who missed the 54-hole cut because more than 78 players made it to the weekend.
Andrew Putnam took the lead over Kuchar as the two began their third round as the one-time PGA Tour victor impressed.