Koepka is going for a season-high third victory in LIV Golf this season, though his seven finishes out of the top 10 in the 54-man league has left him too far behind to challenge for the individual title and the $18 million ($A27 million) bonus.
The race is between Jon Rahm and Joaquin Niemann.
Niemann had a 68, making five birdies but slowed by a double bogey on the par-4 15th hole at Bolingbrook Golf Course. Rahm made only two birdies in his round of 69.
Koepka, a five-time major champion, already has a league-high five career victories in the Saudi-funded league.
He has won this year in Singapore and the Greenbrier. He is four shots ahead of Paul Casey, with Anirban Lahiri another shot behind.
Lucas Herbert fared the best from the Australian contingent. He shot a two-under 68 that included three birdies and a bogey.
Matt Jones is at one over, while Cam Smith and Marc Leishman made 73 and 74 respectively.
After a disappointing opening round, the Australians - Ripper GC - are in 10th position at two over, 11 shots behind Crushers GC, comprising captain Bryson DeChambeau, Paul Casey, Anirban Lahiri and Charles Howel III.
