Second round leaderboard:
-8 J Day (Aus) -7 K Streelman (US), V Taylor (US) -6 S Cink (US), M Laird (Sco), J Senden (Aus) Selected others: -5 P Harrington (Ire) -4 P Casey (Eng), T Woods (US) -1 J Rose (Eng), L Donald (Eng) level R McIlroy (NI), I Poulter (Eng) +4 P Mickelson (US)
Day shot a second successive four under par round in New Jersey
Australia's Jason Day shot a second-round 68 to lead on eight under at the halfway stage of the Barclays, the first event of the US Tour's FedEx Cup.
Overnight leader Tiger Woods moved to eight under with two birdies but the world number one bogeyed four of his last eight for a 73 and is four adrift.
World number two Phil Mickelson carded a three-over-par 74 to miss the cut.
Padraig Harrington and Paul Casey ended five under and four under respectively to boost hopes of a Ryder Cup wildcard.
The duo are among four European golfers hoping to nudge Ryder Cup skipper Colin Montgomerie into picking them as one of his three captain's picks for Celtic Manor in October.
Triple major winner Harrington improved his claim by following his opening round of 69 with a three-under-par 68.
The Irishman, who made six birdies, said: "After missing the cut in the [USPGA] the last thing I wanted was to come here and miss the cut-off or play poorly and then say, well, maybe I'm out of form.
"I believe that Monty should make a decision based on the full year and who is going to play consistently and who we can rely on to play well.
"But in the last tournament of the year, a couple of days before the team is going to be picked, it's nice to be showing a bit of form. It won't do me any harm. It's no burden to carry it, let's say."
Casey added a second successive 69, while fellow Englishman Justin Rose, who is also hoping for a wildcard, was two under for the day to make the cut by a shot at one under.
Their countryman Luke Donald had three bogeys and two birdies on his card as he fell back to level par alongside compatriot Ian Poulter, who has already sealed his Ryder Cup spot.
Woods went into the tournament ranked 112th in the FedEx Cup rankings and needs to finish in the first 57 in New Jersey to move into the top 100 and play in the next tournament in the four-event play-offs, the Deutsche Bank Championship in Boston.
He is also looking to earn a wildcard pick for Corey Pavin's US Ryder Cup team.
The 34-year-old looked to set to capitalise on his opening round of 65 when he moved to eight under par after his opening nine holes.
But a string of bogeys, one featuring an uncharacteristic missed putt from 20 inches, on his homeward nine dropped the American back, although he remains firmly in contention.
"I hit the ball just as good today as I did yesterday," said Woods.
"But I didn't putt well at all. I didn't have the speed at all on the greens. I was leaving it way short or blowing it by the hole. I couldn't figure out the speed."
Mickelson is already assured of playing in Boston because he was fourth in the qualifying standings entering the tournament.
Kevin Streelman shot the low round of the day to join fellow American Vaughan Taylor in second place after sinking nine birdies in an eight-under-par 63.
Australia's John Senden had led on nine under after five birdies on the front nine, but he double bogeyed the 16th after smashing his ball out of a greenside bunker over the back of the green, to fall back to six under par.
Scotland's Martin Laird birdied the last three holes to join Senden and America's Stewart Cink two shots adrift of the leader.