Dustin Johnson is on top of leaderboard at the halfway stage of the Northern Trust.
The American is one shot ahead of Jordan Spieth after two rounds of the PGA Tour's play-off event.
Meanwhile Tiger Woods was forced to withdrew before Friday's round because of "mild oblique strain that led to pain and stiffness".
The third round gets underway later on Saturday.

World Sports Summit showcases Dubai’s pull as global hub for sporting icons
Pakistan's Afridi out of Big Bash League with knee injury
Injured Aubameyang to miss international swansong
Recovering Archer in England squad for T20 World Cup
Forest lodge complaint over officiating in Man City defeat
