Dustin Johnson has joined Roberto Castro at the top of the leaderboard at the BMW Championship after shooting a second-round 63.
The world number two hit five birdies and two eagles as he carded a course record in Indiana, but Castro remains in first spot after a second successive 65.
The pair hold a three-shot advantage over Paul Casey, who continues to show the same kind of form that saw him finish in second place at the Deutsche Bank Championship at the start of this week.
JB Holmes and Chris Kirk share fourth position, while Sergio Garcia is one of four players who sit in a tie for fifth place although they remain seven shots off the lead.
Northern Ireland duo Rory McIlroy and Graeme McDowell are both in 19th spot alongside Jason Day and Jordan Spieth, but Justin Rose is down in 56th position.
