Lahiri bogeyed the 460-yard par-4 sixth, getting on the green in 2 and three putting, moving him to one-over for the round.
Kuchar maintained his lead through the back nine as Putnam began to trail by more with a bogey on the par-4 16th.
Kuchar has also been in fine form after ending a three-year title drought by winning the Mayakoba Classic in Mexico late last year.
Kuchar was at 14-under 126, matching the lowest 36-hole score of his PGA Tour career.
Keith Mitchell had a 63 to pull within four shots, along with Chez Reavie, who fell back with three straight bogeys early on the back nine.
Kuchar led by two overnight and had just one blemish on his scorecard over the first 54 holes, but his customary composure slipped early on the final day at Waialae Country Club as he endured a torrid run of three bogeys in four holes.
Padraig Harrington named Ryder Cup captain
Padraig Harrington poses with the Ryder Cup after being appointed as the European Ryder Cup Captain for The 2020 Ryder Cup . Padraig Harrington has been named captain of Europe's Ryder Cup team for the 2020 match at Whistling Straits in Wisconsin.
Kuchar's final-round 66 put him at 22-under 258 for the tournament, with Putnam finishing at 18 under with a 2-under 68 on Sunday. Kuchar followed with 12-foot birdie putts on the next two holes, and he was on his way to his ninth career victory. "But I kept plugging along, and I knew good things were going to happen". Just needed to make some better swings.
"I'm feeling a little let down right now", Putnam said after closing with a 68. "I have to stay aggressive".
"Certainly a year ago was disappointing, but to win two out of three events is insane to comprehend", Kuchar said.
Putnam, who won the Barracuda Championship last summer and was runner-up to Dustin Johnson at the FedEx St. Jude Classic, moves into the top 50 in the world for the first time in his career at No. 45.
American Kuchar - who is chasing his first win since November - remains in control following his four-under-par 66 at Wai'alae Country Club in Honolulu. You don't get many chances like that and it was nice to be there and been able to finish it off. ...
Australia's Marc Leishman finished in a four-way tie for third place at 17 under with Canada's Corey Conners and Americans Hudson Swafford and Chez Reavie. "I look forward to the rest of the year to try and continue to see how great this year can be".
It was a hard day for 11-time PGA Tour champion Spieth, who had four bogeys and just one birdie to be tied for 127th and 12 shots off the pace. But, his standing atop the leaderboard was threatened by one-time victor Andrew Putnam.