American Homa, who won by four strokes last year, sunk eight birdies in all, but dropped shots on the 13th and 15th holes looked to have tarnished his solid start.
"I thought I played really well. It was really tricky with the wind, it did a complete flip on seven, so it threw us through a bit of a loop but I thought I did a really good job of adjusting to it," Homa said.
"I made one mistake on the 15th, leaving it long of that pin, but otherwise I did a pretty good job of playing within myself and not hitting shots I don’t love to hit, so yeah, it was good."
He is one shot ahead of South African Ockie Strydom, who managed an eagle on the par 5 14th hole in his five-under-par round of 67.
Spaniard Pablo Larrazabal is one of four players a further two shots back in tied third on three-under-par.