Padraig Harrington shot to the top of the leaderboard at The Barclays in Farmingdale but even victory this weekend may not be enough to earn him a place on Europe's Ryder Cup team.
Harrington, searching for his first US tour title since the 2008 USPGA Championship, recorded a superb seven-under-par 64.
He leads by one stroke from Americans Nick Watney and Brian Harman.
The Irishman cannot qualify by right for Jose Maria Olazabal's team but may be a contender for a wild card, although Ian Poulter seems sure to land one of the captain's two picks for next month's match at Medinah.
Harrington had eight birdies, including six of the last seven holes, in his seven-under round on the par-71 course.
But Olazabal, at Gleneagles this week for the Johnnie Walker Championship, said it would take "at least" a victory for Harrington on Sunday to put him in the frame for selection on Monday.
"I don't know where I sit. Or maybe I do," Harrington, who turns 41 next week, said to laughter in his press conference.
"I'm not really going to get into and discuss because I'm either going to do one of two things: I'm either going to look like I'm pleading or I'm going to look like I'm incriminating myself, one or the other.
"As I keep saying to people, you over here have this thing called the Fifth (Amendment). I'm going to plead the Fifth.
"I'm not going to build myself up or I'm not going to tear myself down. At the end of the day, it's up to him."
Harrington was asked if "an incident that occurred nine years ago" could influence Olazabal.
At the 2003 Seve Trophy, the pair had a notable argument over a rules issue.
"You really have done your homework," Harrington said.
"I was very supportive of Jose when he got the captaincy. I truly believe that he's interested in winning the Ryder Cup. From the character that he is, I believe he would put winning way above anything that's personal."
In-form Spaniard Sergio Garcia was shaping up for another title challenge after ending his long drought at the Wyndham Championships last week, as he checked in at five under for a share of fourth place alongside England's Gary Christian.
Justin Rose stood four under, in a group containing Rickie Fowler, Dustin Johnson and KJ Choi, while one shot further back Tiger Woods was alongside his fellow multiple major winners Phil Mickelson, Ernie Els and Vijay Singh, plus Englishmen Greg Owen, Luke Donald and Poulter.
Woods played alongside world number one Rory McIlroy who posted a two-under 69, the same mark as Lee Westwood.
McIlroy was asked about Harrington's performance, and can understand why a victory for the Dubliner this week could cause Olazabal to stop and consider his choices.
McIlroy said on pgatour.com: "I saw him atop the leaderboard, giving Jose something to think about at least."