The key was a 16-foot eagle putt at the par-five 13th that ignited his round -- and none too soon.
"I'd been waiting for my first birdie for quite awhile, after 12 holes, one bogey and 11 pars," he said.
"After my drive on 13, I ended up in the right rough but (at) quite a good number for my 3-iron.
"The greens are quite soft, so I could land it in the middle of the green, into the slope, bring the ball down close to the flag.
"I got about 16 feet and holed the putt, which is one of the best putts so far."
He followed up with birdies at 15 and 16 and shared sixth place behind overnight leaders Bryson DeChambeau and BrooksKoepka.
The 29-year-old from Thailand, playing the Masters for the third time, said he's still a long way from feeling comfortable at Augusta National, where danger lurks among the lush landscape.
"Not really," he said. "If you go for it too much, it might hurt a lot. A couple of holes give a chance, but you have to be really careful."
Kiradech, whose four European Tour victories include last year's Handa World Super 6 in Perth, was delighted with his position as he vies to improve on his previous best Masters finish of equal 15th, achieved in 2016.
"Really happy with the way I started," he said. "Three-under here is not easy at all. You have to be solid every single shot, hole the putts. This course can hurt you a lot."