|Northern Trust second-round leaderboard|
|-12 D Johnson (US); -11 J Spieth (US); -10 T Merritt (US), P Reed (US), A Ancer (Mex), J Rahm (Spa)|
|Selected others: -9 J Rose (Eng), L Oosthuizen (SA); -8 I Poulter (Eng); -7 R McIlroy (NI); -6 S Lowry (Ire); -4 T Hatton|
American Dustin Johnson holds a one stroke lead after the second round at Liberty National in the first of the PGA Tour's play-off events.
The world number two birdied the 18th to move ahead of compatriot Jordan Spieth on 12 under par in New Jersey.
Former US Open champion Johnson, 36, followed up a 63 on Thursday with a four-under 67 in the second round.
Tiger Woods withdrew before Friday's round because of “mild oblique strain that led to pain and stiffness”.
Three-time major winner Spieth carded a seven-under-par 64 in which he made eight birdies, the only blemish a bogey at the 18th.
That was the first dropped shot of the Northern Trust for the 26-year-old after a bogey-free 67 on Thursday.
Johnson opened with a bogey but hit back with successive birdies through three and four and clawed back three more strokes after the turn.
Justin Rose sits three shots off the lead with fellow Englishman Ian Poulter a further stroke back, while Northern Ireland's Rory McIlroy sits at seven under par.
Woods withdraws with side problem
Woods struggled to a four-over-par 75 on Thursday during his first round since missing the cut at The Open last month and then withdrew before his second-round tee time.
The 15-time major champion, who had spinal fusion surgery in April 2017, said he went for treatment for a problem on his side “early Friday morning”.
“But unfortunately I'm still unable to compete,” added the 43-year-old.
“I'd like to thank the New Jersey and New York fans for their support and remain hopeful I can compete next week at the BMW Championship.”
The American was only able to practise chipping and putting in Wednesday's pro-am and joked that at least he had broken 80 during Thursday's opening round.
Woods has played a very limited schedule since he won the Masters, with this only his fifth start since that victory in April.
His fifth Green Jacket capped a comeback from four operations on his back which saw him drop to world number 1,199.