The 25-year-old, whose best finish last season was a tie for 39th, was trailing clubhouse-leader Andrew Putnam but leapfrogged him after four consecutive birdies on the back nine and one final one on the par-five 18th hole.
Kooch, who opened with rounds of 63-63, stayed on track with three birdies on the front nine and carded a 54-hole score of 18-under 192.
Kuchar was sliding his way out of the top 50 toward the end of previous year, when he failed to make a Ryder Cup or Presidents Cup team for the first time since 2009. He won the Match Play Championship and the Memorial in 2013.
Canada's Corey Conners, who got into the field through a Monday qualifier, had a 64-64 weekend and was among four players who tied for third, though none had a serious chance of challenging what amounted to a two-player race at the top.
But this day ultimately belonged to Kuchar, who won for the ninth time in his career.
Kuchar, who had been winless for almost four years until his win at the Mayakoba Classic late in 2018 now appears likely to add a 9th PGA Tour title just three months after his 8th.
"I loved the fight", Spieth said. With no bogeys on his card, it even felt easy to him.
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Marc Leishman (64), Hudson Swafford (64) and Chez Reavie (67) also finished in a tie for third. He's a victor again, and for a guy who loves Hawaii, he was thrilled to already have a spot reserved at Kapalua for the winners-only field 50 weeks from now. He finished top five in both events, and following his win last fall at the CIMB Classic should be considered one of the players best positioned to break into the upper crust of golf as we head toward the heart of the season. He also beat Patrick Reed and Ian Poulter, who are both only 15 years younger than Love but also played in the Ryder Cup. Obviously previous year was disappointing, but to win two out of three events is insane to comprehend.
"Before the other two I just hit the shot and I was trying to see if it was going at the hole".
Indian golfer Anirban Lahiri ended with a one-over 71 in the third round of the Sony Open in Honolulu, Hawaii, which saw him drop to three-under 207 for a tied-63rd spot on Saturday.
Matt Kuchar remains in control following his four-under-par 66 at Wai'alae Country Club in Honolulu.
Andrew Putnam was two shots behind after a 67.
Matt Kuchar hits from the 10th fairway during the second round of the Sony Open on Friday. He used eight birdies to complete the feat, including three on his final seven holes.