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.

England beat New Zealand to keep Pakistan's T20 World Cup hopes alive
Medvedev to face Griekspoor in bid for second Dubai title
Real Madrid face Man City again in Champions League knockouts
India defeat Zimbabwe to revive T20 World Cup hopes
Auger-Aliassime sets Medvedev semifinal in Dubai