"To shoot seven-under back-to-back is unexpected, but certainly awfully exciting", said Kuchar, who finished his front nine by making an eagle on the par-five hole.
Beneath that cap is plenty of gray hair.
Putnam, who played college golf at Pepperdine and claimed his first PGA Tour victory a year ago in the Barracuda Championship, capped his 67 with an eight-foot birdie putt on the last hole. It's not often you're in full control.
Keith Mitchell fired a seven-under 63 and is tied for third with Chez Reavie (66) on 196.
The only other time Kuchar won twice in the same season was in 2013, when he won the Match Play Championship in Arizona in February and the Memorial in early June.
Kuchar ended a four-year drought by winning the Mayakoba Classic in Mexico last fall, and there are a few similarities.
Kuchar ended a almost five-year drought when he won the Mayakoba Classic in November, his eighth PGA Tour win, and he said it was a good recent experience to have in the memory bank.
"Didn't feel as easy as the first two days, " Putnam said. Putnam birdied No. 18.
Meanwhile, USA's Matt Kuchar looked in fine form as he maintained his lead at the top of the table which saw him keep another clean card and shoot a 4-under 66 to take a two-shot lead into the final round of the Sony Open.
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. "Still played a good round. Still got a chance".
- PGA TOUR (@PGATOUR) January 13, 2019 " rel="noopener noreferrer" target="_blank" tied his career low round of 63.
Also tied for fifth were Charles Howell III and 54-year-old Davis Love III, who had one of his better putting rounds.
Kuchar was at his best on a number of putts from the 50-foot range.
Veteran Kuchar has a career-best 54-hole score in Hawaii as the American tries to win for the ninth time on the US PGA Tour.
"I'm just going to stay aggressive".
The PGA Tour only began keeping hole-by-hole records in 1983, and no one had ever made three eagles in one round on par 4s since then. He's also No. 1 in the field in strokes gained on approach shots for the week.