Cameron Smith has given another indication of his mental toughness with a comeback win at the World Golf Championships Dell Matchplay today in Austin, Texas.

But Jason Day and Marc Leishman suffered early defeats in the round robin section, Day losing 2 down to American Scottie Scheffler and Leishman 2 and 1 to Victor Perez of France at Austin Country Club.

Smith came from behind to beat American Lanto Griffin 1 up at the 18th hole.

The Queenslander, ranked 27th in the world, was two down to the American through 15 holes. But at the par-five 16th he made a birdie from four metres to win the hole, at the 17th Griffin conceded after finding a terrible lie in a greenside bunker, and then Smith took the 18th with a par to complete the win after Griffin imploded at the green.

The American thinned a chip through the green and then chunked the next just a few centimetres forward to hand the win to the Aussie.

"I thought it was pretty solid," he said afterward. "(I) hit a couple in the water, which really kind of let me down, especially through those middle holes there where you can apply some pressure and it was good to come back and get the win there."

Smith plays matchplay beast Ian Poulter tomorrow after Poulter flogged Rory McIlroy in the first round today, 6 and 5.

"'Poults' and I get along," said Smith. "I'm sure we're going to have a good time. In the last five or six holes we'll quit talking to each other and it will be on. So, no, I'm looking forward to the challenge tomorrow for sure."

Leishman has been out of form and he was not at his best again Perez, who took control at the 12th where the Australian went for the green with his second shot at the par-five and unluckily kicked off the putting surface and into water.

At the 16th, another par-five, the Frenchman pulled driver off the deck from 240 metres and found the green with his second to put an exclamation mark on it.

Day was never in front in his match against Scheffler today and the Australian bogeyed two of the last three holes to lose 2 down. He has another tough one against Presidents Cup star Xander Schauffele tomorrow.

The other Australian, Marc Leishman, was engaged in a tight match against Frenchman Victor Perez.

The biggest surprise of the day was Antoine Rozner of France beating world No. 5 Bryson DeChambeau 2 up.

Tomorrow’s Australian matches:

Cameron Smith v Ian Poulter (England) Marc Leishman v Sungjae Im (South Korea) Jason Day v Xander Schauffele (USA)