• Koepka, who led by two going into the final round, signed for a 75.
• Former champions Jordan Spieth and Patrick Reed were a shot further back.
Image: /FILE
Spain's Jon Rahm kept his nerve and patience to win a first Masters, swinging an exciting final day in his favour from American Brooks Koepka.
Rahm, 28, carded a three-under 69 to finish on 12 under and win by four shots as Koepka, who led by two going into the final round, signed for a 75.
Koepka ended joint second with veteran Phil Mickelson, who shot a a stunning seven-under 65 to finish eight under.
Former champions Jordan Spieth and Patrick Reed were a shot further back.
Defending champion Scottie Scheffler finished in a group on four under, along with England's US Open champion Matt Fitzpatrick, who was the highest finisher from Great Britain and Northern Ireland.
Rahm became the fourth Spanish player to win the Masters and his victory poignantly came on what would have been the 66th birthday of the legendary two-time champion Seve Ballesteros, who won in 1980 and 1983.
"I wasn't sure how [the emotion] was going to come to me until I hit the third shot on the 18th," said Rahm, whose first major win came at the 2021 US Open.
"History of the game is a big reason why I play and Seve is a big part of that history.
"For me to get it done on the 40th anniversary of his second Masters win and on his birthday was incredibly meaningful."
How Rahm took control to win Green Jacket
Rahm was one of the pre-tournament favourites - alongside Northern Ireland's Rory McIlroy, who missed the halfway cut, and world number one Scheffler - after an impressive year in the lead-up to the first men's major of the season.
With three wins on the PGA Tour this year, plus four top-10 finishes in six previous Masters starts, Rahm had the form and previous pedigree to win at Augusta - and he duly delivered.
Remarkably, he started his bid on Thursday with a double bogey after a four-putt on the first hole. After that he barely made a wrong move.
Rahm showed all facets of his outstanding all-round game - particularly his relentlessly huge driving and nerveless putting - to record an opening round of 65 and then posting scores of 69, 73 and 69.
Not only did Rahm win the iconic Green Jacket for the first time, he also returned to the world number one ranking.
Leading by four shots with four holes left to play, he maintained that advantage going into the 18th hole and could even afford to hit his final drive into the trees.
The ball ended up bouncing back into play and landing 150 yards from the tee, but he retained composure to lay up and knock a sublime chip to within a few feet for an unorthodox par.
"It was a very unusual par, very much a Seve par - in a non purposeful way. I know he was pulling for me and it was a great Sunday," added the 28-year-old.
After sinking his final putt, Rahm shook his clenched fists while looking up to the sky.
His family - wife Kelley, along with two sons Kepa and Eneko - quickly joined him on the 18th green before he was congratulated further by friends and family.
Those included compatriot Jose Maria Olazabal, another two-time Masters champion and one of Rahm's mentors.
Koepka fades as LIV denied victory
What looked set to be a tight two-way duel between Rahm and Koepka ended up being a controlled and clinical victory for the Spaniard.
As well as Rahm's brilliance, a poor final round from Koepka was a significant factor.
Koepka was bidding for a fifth major title - and a first since 2019 - despite barely having played 72-hole events in recent months after deciding to switch to the controversial Saudi-backed LIV Golf tour.
The LIV tournaments are played over 54 holes, although Koepka arrived at the Masters in form having won last week's event in Miami where his $4m (£3.2m) prize, exceeded the record $3.24m Rahm will take home for winning the first major of the year.
But his driving became wayward early in the final round and once that allowed the momentum to shift towards Rahm, Koepka could not recover.
Asked by Sky Sports how he felt after being unable to maintain his lead, Koepka said: "Kind of ho-hum. I didn't play that great. I hit some good shots and just ended up in some terrible spots. Then at the end trying to make birdies when he's ahead - it's tough.
"Second is not very fun so that's motivation in itself."
Mickleson and Spieth roll back the years
In front of the final pair, a dramatic battle began to build as a host of former major champions jostled for position and threated to take advantage of any slip-ups.
Three-time Masters winner Mickelson, 52, surprisingly became the main challenger after a scorching run of five birdies in the final seven holes.
Mickelson skipped last year's tournament because of a self-imposed break from the sport, after he made controversial comments about the Saudi-backed LIV project which he eventually joined.
But he looked like his old self as he took the acclaim of the Augusta patrons after the final birdie moved him into the clubhouse lead.
It also lifted him into joint second place alongside fellow LIV player Koepka, remaining there to become the oldest player in Masters history to finish in the top five.
"This is as much fun as I could possibly have playing golf," he said.
"The final round of the Masters and to play the way I did and finish with a couple of birdies, regardless of the outcome, it has been a fun day.
"I'm grateful to be here and compete, to be part of this great Championship and to play how I did was extra special."
Mickelson finished a shot ahead of playing partner Spieth, with the 2015 champion also racing up the leaderboard after starting with two birdies and adding three on the bounce around the turn.
Reed, the 2018 champion and another to move to LIV, had a double-bogey seven on the second hole but responded with eight birdies on his way to a 68 as he joined Spieth on seven under, in a share of fourth place, with another American Russell Henley.