Roberto Castro's overnight lead of one shot held up when the rain-delayed first round of the BMW Championship was completed on Friday in Carmel, Indiana.
Castro, one of 33 players in the 69-man field to complete the opening round on Thursday before weather halted play, fired a seven-under-par 65 that left him one stroke in front of American compatriot Brian Harmon.
U.S. Open champion Dustin Johnson, former PGA Championship winner Jason Dufner and Englishman Paul Casey were among five players who started out with 67s in the third of the PGA Tour's four playoff events that conclude the season.
A confident Rory McIlroy, fresh off his victory at the Deutsche Bank Championship on Monday, returned early on Friday morning to complete the final eight holes of his first round.
The Northern Irish world number three, who was three-under after 10 holes on Thursday, mixed a bogey with two birdies over his closing stretch to finish three shots off the pace.
Fourth-ranked Jordan Spieth and fellow American Phil Mickelson, a five-times major winner, also opened with 68s
Only the leading 30 players in the FedExCup standings after this week's event will advance to the Sep. 22-25 Tour Championship finale in Atlanta.
(Reporting by Frank Pingue in Toronto; Editing by Mark Lamport-Stokes)