Lydia Ko jumps in the lake by the 18th to celebrate winning the first LPGA Tour major of 2016.

New Zealand golfer Lydia Ko has celebrated winning consecutive LPGA major titles with a leap into the lake by the 18th.

Ko, 18, held her putting nerve to win her second consecutive major title in dramatic fashion in the United States on Monday.

The world No 1 fired in a final round 3-under 69 to finish the ANA Inspiration at 12-under and win by one shot, time and again nailing crucial putts to keep her chances alive.

Kelvin Kuo/ USA Today Sports Lydia Ko celebrates winning the first LPGA Tour major title of 2016 with a leap into the lake.

Ko sunk a massive birdie putt on the 8th, then strung together par saves on the back nine for a three-under 69 that was one shot too good for Englishwoman Charly Hull and Korean In Gee Chun.

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Crucially she sunk a long putt on 17, after missing the green off the tee then sealed the deal with a magnificent approach shot on the par 5 18th, leaving herself close to a gimme for victory.

Kelvin Kuo/ USA Today Sports Lydia Ko kisses the ANA Inspiration trophy.

Yet again she showed her mettle when Thailand's Ariya Jutanugarn looked to have her measure over an enthralling exchange at the Mission Hills Country Club in California.

After leading by two shots deep into the round, Jutanugarn dropped three shots in the last three holes - a penalty for hitting into the water on the 18th ruining her chances once and for all, she was to finish fourth two shots adrift of the Kiwi.

And so Ko held strong for glory.

LPGA Lydia Ko makes birdie on the 18th to set up a one-stroke victory in the first LPGA Tour major of 2016.

"This has been a long week, I'm proud I was able to make those clutch putts on the back nine," Ko said.

"For these amazing things to be happening, it's incredible."

The victory made Ko the second-youngest winner of the event, just the third player to win this major and the preceding LPGA Tour event, the first to claim Tour wins in back-to-back weeks since Inbee Park in 2013, and the second youngest double major winner in history.

GETTY IMAGES Lydia Ko follows the fortunes of a drive during her final round at the ANA Inspiration.

Scotsman Young Tom Morris won the 1868 and 1869 British Opens - he was 17 when he claimed his first. Ko is widely acclaimed as the youngest dual winner of modern history.

Ko was 18 years, 11 months, 9 days when she won.

As for the traditional leap into the lake at the 18th after winning, she had no idea how she would go about that.

KELVIN KUO Lydia Ko with her second major trophy.

"I don't know, I've never imagined it," she said.

"Just as long as I don't break anything."

Self-preservation was cast off as she made the leap, with her mother, sister, caddy Jason Hamilton and his fiancee also taking the plunge.

Ko at least got to don a dressing gown after taking the plunge.

"This is an unbelievable moment. I've always walked out on the bridge and have seen Poppie's Pond and said, 'Wow that is super clear and how amazing would it be to just jump in there.'

"Earlier this week, Abby [Wambach] jumped in there after Danielle [Kang] chipped in for eagle. I thought, 'Hey, how do you beat that kind of jump?' It is an amazing moment. Being here with the team makes it even more special."

Commentator Judy Rankin said it had looked as if it would not be Ko's day, yet somehow she turned it around.

"She wasn't looking like someone who was knocking the flagstick down and making birdies, but what she did was she saved herself several times at such important times. She locked it up with that little wedge at 18.

"She is one of the most amazing players I've ever seen, and I've only been seeing her since she was 15, so I've had a short history.

"She is really beautiful to watch and she has the kind of swing, the kind of stroke, that I think people can imagine when they swing the club how they would like it to be.

"She has the most ideal temperament I have ever seen."

TENSE FINAL ROUND

Both Ko and Jutanugarn had started the day a shot behind Lexi Thompson and while the American drifted off the pace badly with a bogey-riddled performance to finish in a tie for ninth, Ko and Jutanugarn kept their duel going.

Ko was spotless in terms of bogeys but could only manage to birdie both the par threes on the opening nine.

Jutanugarn mixed five birdies with a bogy through 15 holes to open up a two-shot lead over Ko after they had been tied at 11-under at the turn.

But Jutanugarn bogeyed the par four 16th with a three-putt to open the door fractionally to Ko who was playing a hole ahead of her.

While Ko kept her nerve, Jutanugarn's game started to unravel. She hit her tee shot at the par-three 17th into a bunker and went past the hole with her sand shot, leaving her with a three-metre putt for the save. She missed that and had to settle for a bogey to tie up the lead.

Ko played safe on 18th, a par-five that had been offering plenty of birdies. She laid up with her second shot and hit her third to win 30cm of the pin for her birdie and a one-shot lead to apply all the pressure on Jutanugarn.

Jutanugarn put her tee shot in the water and had to lay up with her third. She couldn't get close to the pin and Ko had the title.

The pressure had been increased by Hull and Chun also finishing at 11-under in a tense final hour of play that saw them eventually end in a tie for second as Jutanugarn's game collapsed.

Ko was coming off victory at the Kia Classic last week, her 11th LPGA title.

Ko's breakthrough first major championship came last year in September in France when she claimed the Evian Championship.

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