The par five ninth at the US Open might be the hole that fractured Lydia Ko's relationship with caddie Jason Hamilton.

Ko has split with the Australian who has carried her clubs since the end of the 2014 season, culminating in 13 titles including two major wins.

Ko's coach David Leadbetter revealed to Radio Sport that Ko and Hamilton separated last week, which has affected her during a recent form slump.

"I think that's been on her mind a little bit. The reasons are a little uncertain at the moment. They felt they weren't getting on together, it wasn't acrimonious in any way," Leadbetter told Radio Sport.

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Ko took on the Hamilton, who previously worked with former world No1 Yani Tseng, at the start of last year after auditioning eight caddies.

Ko will use a couple of temporary caddies for the remainder of the 2016 season.

A double-bogey that saw Ko squander the lead at the US Open might be the reason behind the break-up. Ko held a one-shot lead going into the hole but recorded a seven on the par five before going into finish in a tie for third with a final round three-over 75.

"Sometimes I've found with young players they can become too reliant on their caddie," Leadbetter said.

"At the US Open I felt she should have won that tournament and I think she made a poor decision and I think she relied on her caddie to make it. A lot of times, more experienced players will make a decision and go for it. I think she got talked into a shot on the ninth hole, a par five where there was no way she should have gone for it. She should have layup and she made a double [bogey] on the hole."

American Brittany Lang won the tournament after beating Sweden's Anna Nordqvist in a controversial three-hole playoff.

Hamilton has told the Golf Channel that he's already signed up with world No 8 Ha Na Jang.

"She told me in the clubhouse after the round [at the KEB HanaBank Championship] that she felt like now was a good time to make a change," Hamilton told GolfChannel.com.

"She said she thought it would be good to get a different set of eyes out there."

"These things happen, it's part of the game," Hamilton said.

The world number one's been unable to hit her usual lofty heights of late, with just one top five finish from her last five tournaments. She produced her worst result of 2016 in the weekend after finishing well back at the in South Korea, in a tied for 51st.

It's now a matter of finding the perfect caddy for Ko, as she and Hamilton were a great team, Leadbetter added.

"I'm sure next year, whoever it may be, she'll have a good caddie. Every man and his dog wants to caddie for Lydia. They're going to make a lot of money. She's going to get one of the better caddies whether it's from the LPGA or the PGA tour."

"She's very easy to work with. She's not overly demanding and she's a pleasure to be around."

Leadbetter said it's fair to say Ko has gone through a bit of a form slump of late following four victories earlier in the season, followed by a silver medal at the Rio Olympics.

"I honestly think, and you're probably seeing this with a few other players, that fatigue is definitely setting in. The Olympics really took a lot out of her," Leadbetter said.

Despite her drop in form, Ko remains the world number one and lead the Race to the CME Globe standings, which features a $1m prize. She has won the CME Globe title the last two years. She lies second in the Rolex Player of the Year points standings, four points behind Thailand's Ariya Jutanugarn.

"She's had a heck of a year regardless. She's 19, she's still learning how to handle and how to manage herself, how to balance things. It's the first little slump she's had over the last four years. Fortunately she played so well over the first two-thirds of the year."

"It's nothing major. She's just a little flat at the moment."

Leadbetter said Ko will take a week off and skip the Blue Bay LPGA event in China before looking to finish the year strong heading into the season finale at the CME Group Tour Championship in Florida.