DUSTIN JOHNSON RATTLED in a monster eagle putt at the first playoff hole to win the LIV Golf Invitational Boston, upstaging the raft of newcomers to the breakaway circuit.

Johnson emerged triumphant from a three-way playoff that also featured Chile’s Joaquin Niemann and India’s Anirban Lahiri, both making their debuts in the controversial Saudi-backed series.

All three finished 54 holes at International Golf Club on 15-under par.

World number two and reigning British Open champion, Cameron Smith, finished a shot back on 14-under in his LIV Golf debut, tying for fourth with England’s Lee Westwood, who charged into contention with an eight-under par 62 but bogeyed his last hole to miss the playoff.

Johnson carded a five-under par 65 on Sunday, his sixth birdie of the day at the 13th, putting him atop the leaderboard at 15-under.

He wouldn’t make another birdie, however, needing par saves at the par-three 17th and 18th to make the playoff.

Johnson didn’t hold back on his playoff putt, sending it racing up the hill. The ball hesitated when it hit the lip, then hit the back edge of the cup and bounced in.

“Yeah, it was going a little fast, but it was a good line,” said Johnson, adding he felt the 18th “owed me one” after his second shot in regulation ended up in the underbrush alongside the giant scoreboard behind the green.

Lahiri was first in the clubhouse on 15-under, and could have sealed the win at his final hole of regulation, the 18th, where his six-foot eagle putt circled the cup but didn’t drop.

His six-under 64 featured an eagle and six birdies, but after finding the fairway at the first playoff hole, he missed the green with his second shot.

He chipped to five feet for a birdie chance only for Johnson to seal the win.

Niemann booked his playoff spot with his fifth birdie of regulation at the 18th. But his tee shot in the playoff hit a spectator before settling in the right rough, and he was in a greenside bunker from there.

Johnson, who finished eighth in the inaugural LIV Golf event in London, fourth in Portland and third at Bedminster, became the first American to lift the individual trophy in the series.

He pocketed a $4 million first prize along with $750,000 as his share of the team first prize for his 4 Aces outfit, which finished two strokes better than Lahiri’s Crushers.

The massive purses, along with reported signing bonuses to top players, have the established PGA Tour and DP World Tour scrambling to retain their talent — the PGA Tour promptly banning any player who tees it up in LIV Golf even as they move to create more lucrative events on their own circuit.

LIV Golf, backed by the almost unlimited resources of Saudi Arabia’s sovereign wealth Public Investment Fund has also been accused of “sportswashing” the kingdom’s human rights record.

Despite the critics — and increasing bad blood between LIV Golf defectors and PGA Tour stalwarts — Johnson said he was happy to be a part of what he sees as an exciting new venture.

He said the money on the line made for plenty of competitive tension, despite the freewheeling atmosphere.

“Especially with that check that you get — you can feel it,” Johnson said.

American Pat Perez, who claimed the most recent of his three US PGA Tour titles in 2018, has reaped the rewards of the 4 Aces’ three team victories so far, earning $750,000 for each.

He had a succinct answer for critics who say LIV Golf’s tournaments amount to exhibitions.

“Exhibition match don’t pay $4.75 million,” Perez said.