Rory McIlroy's impending divorce clearly ain't affecting his golf game ... the PGA Tour star just lit up his first round at the PGA Championship.
Hitting the course for the first time since he filed for divorce on Monday from Erica Stoll, McIlroy showed no signs whatsoever of being off -- carding a 5-under 66 at Valhalla Golf Club in Louisville, Kentucky.
Following the end of his round, he was in a tie for third .