Justin Thomas labelled Saturday's halved match against Marc Leishman and Abraham Ancer "unacceptable" after he and Rickie Fowler sensationally coughed up a commanding lead at the Presidents Cup.

United States pair Thomas and Fowler surrendered a 5up cushion through 10 holes as Leishman and Ancer somehow secured half a point for the Internationals in Saturday afternoon's foursomes in Melbourne.

Thomas and Fowler arrived on the 11th poised to seal a third point for seven-time defending champions the USA, who threatened to sweep the session and tie the Presidents Cup at 9-9.

However, Thomas and Fowler capitulated as the Internationals ended the day 10-8 in front of Tiger Woods' USA heading into Sunday's singles.

"Speechless," Thomas said afterwards. "It's unacceptable for us to get half a point. I mean, they made a couple of long putts there on 15 and 16 to keep it going. 

"We had our chances, and I mean, flat honest, just didn't execute. I'm just disappointed in myself for burning that, I felt like, for us on 18.

"Our team is playing well today, and we've got to put it behind us and go get a point tomorrow."

The match was decided at the last with Thomas' tee shot sailing into the trees, immediately putting the USA on the back foot.

Leishman and the Internationals capitalised after the former's quality approach shot within seven feet set up Ancer - who converted the birdie as the USA could only manage a third straight bogey.

It sparked wild celebrations and Leishman told reporters: "That's probably as good as I've felt on a golf course, and I only halved the match. We've all won up here; we've won tournaments, but we don't get chances to play with a team-mate very often.

"To be successful with a team-mate would be pretty cool. We had a taste of that today, but I think if we can play well and do our jobs tomorrow, what we felt today is going to probably be pushed aside for what we may feel tomorrow. So it ranks pretty high for me."

Leishman added: "I spoke to [captain] Ernie [Els] going down 12, and he was just saying, get as far as you can. Take it as for as you can. I'm like, 'Hang on. Let's not talk about losing this yet. We're going to fight this out', and yeah, we did."