Matsuyama, who started the day with a commanding four-shot lead, carded a 1-over 73 in the final round to hang on for the victory and narrowly fend off a strong group of chasers.
The 29-year-old built a five-shot advantage as he made the turn, but Zalatoris and Xander Schauffele applied pressure on the back nine. Schauffele rattled off three straight birdies on Nos. 12-14 to make things interesting as the last pairing got to No. 15.
On the final par-5 at Augusta, Matsuyama airmailed the green with his approach shot and wound up making a costly bogey. Meanwhile, Schauffele made his fourth consecutive birdie to get within two shots with three left to play.
However, Schauffele took an aggressive line at the pin on the par-3 16th and came up well short. The 27-year-old's hopes were dashed as his ball landed on a steep downslope in front of the green and trickled back into the water.
Thanks to the comfortable cushion Matsuyama built with his stellar play on Saturday and most of Sunday, he was still able to walk away as the champion despite bogeying three of his final four holes.
Matsuyama becomes only the seventh player ever to earn low-amateur honors (2011) at the Masters and win a green jacket later in their career, and the victory also marks his first PGA TOUR title since 2017 and the sixth overall.
Matsuyama's win also completes a sweep for Japan at Augusta over the past two weeks, with 17-year-old Tsubasa Kajitani winning the Augusta National Women's Amateur last weekend in a playoff.
"Hopefully I'll be a pioneer in this, and many other Japanese will follow," Matsuyama said through his translator during the green jacket ceremony in Butler Cabin. "I'm glad to be able to open the floodgates hopefully, and many more will follow me."
Here's how the top of the leaderboard finished at the 85th Masters:
|Place||Player||To Par||R4 Score|
Zalatoris claimed the runner-up position in his Masters debut. The 24-year-old birdied two of his final four holes to move up the leaderboard with his fourth under-par round of the week.
Due to his triple-bogey on No. 16, Schauffele settled into a tie for third with Jordan Spieth.