Koepka warms up for PGA defence with LIV Singapore victory
The 34-year-old American, a five-time major winner, finished at 15-under par to become the first player to win four individual titles on the Saudi-backed breakaway circuit which is in its second full season.
"I feel good. It's a lot better than I did last week," said Koepka, who has hit form at just the right time as he heads to Valhalla to defend the major he won a year ago at Oak Hill.
"It's all starting to come around. I've put in a lot of work and I like the way things are trending," added Koepka
"I just need to go back next week and make sure everything continues, do the right stuff and go from there."
Koepka started the third and final round with a three-shot advantage and did not look like relinquishing it after birdies at the fourth and fifth.
A bogey-five on nine proved to be a temporary blip as birdies on 10 and 15 sealed the victory, despite a charge from Smith, who fired a seven-under 64 to finish on 13-under, and Leishman, who carded a 66.
"I just played very consistently and happy with the way I played all week," said Koepka.
"I made a couple of clutch putts today and the ball-striking was solid. I didn't really think I made too many mistakes. And that's a great feeling when it kind of feels easy."
Smith and Leishman's final-round heroics helped take Ripper GC to a second consecutive team title, a week after they triumphed in a playoff in Adelaide.
The all-Australian team, which also features Matt Jones and Lucas Herbert, won with a 32-under-par aggregate.