Australia’s British Open champion Cameron Smith has claimed his first LIV Golf victory in only his second start on the lucrative Saudi Arabia-backed circuit with a three-shot triumph over Dustin Johnson and Peter Uihlein just outside Chicago.

Smith, one of 12 major champions in the 48-player field at Rich Harvest Farms, shot a three-under-par 69 in the final round of the 54-hole event on Sunday to reach 13 under and secure the $US4m ($A6m) first prize.

“I think I had to prove to probably myself and some other people that I am still a great player, you know I am still out here to win golf tournaments,” Smith said.

“Proud of how I hung in there today. Didn’t really have my best stuff the first eight or nine holes but stuck it tough and made a few good putts coming in. It was nice.”

The stage was set for a final-round duel between two of the world’s best golfers as overnight leader Smith began the day two shots clear of playing partner Johnson (70), who fell three shots back after a bogey at the first hole.

Both players birdied the second hole but Smith bogeyed the fourth and sixth as Johnson got to within a stroke before the duo carded birdies at the par-five seventh.

Smith is the highest-ranked player to join LIV Golf to date and finished fourth in his debut two weeks ago in Boston where he missed out on a three-man playoff by one shot after a bogey on his penultimate hole.