The two Americans on Friday were tied atop the leaderboard on 10-under-par 130 in Greensboro, North Carolina.
Slocum, a four-time winner on the PGA Tour, came into the final event of the tour's regular season trying to play his way into the FedEx Cup playoffs.
He started the week ranked 158th on the playoff points list, with only the top 125 advancing to the Barclays Championship next week.
He got to work early on Friday, in the first group of the day to tee off, and made seven birdies and two bogeys.
"I played great. I hit lots of fairways. Hit some good quality iron shots and my putter again was working," said Slocum, who admitted he was surprised to find the greens at Sedgefield Country Club rolling as fast early in the morning as they had on Thursday afternoon.
"There were some difficult pins out there," said Slocum, who made a clutch four-footer for par at the par-three 12th then birdied the next four.
"It was a good stretch and obviously at this point you're going to need a lot," Slocum said. "You're going to have to have some of that to keep yourself in contention and go for it."
Langley, comfortably within the top 125 in the FedEx Cup rankings at 81st, had six birdies and one bogey to put himself in position to challenge this weekend for a first PGA Tour title.
Andrew Svoboda arrived at 18 with a share of the lead but bogeyed his last hole in a 64 that left him tied for third on 131 with Scotland's Martin Laird and fellow Americans Brian Stuard and Nick Watney. Watney also posted a 64, while Stuard carded a 65 and Laird 66.
- Nine birdies for Ishikawa -
First-round leader Camilo Villegas signed for a 69 that left him in a group of players sharing seventh on 132.
Japan's Ryo Ishikawa joined that group with a sparkling eight-under 62 that included nine birdies and one bogey.
Canadian Brad Fritsch reached 132 with a 63 and Sweden's Freddie Jacobson posted a 64.
Americans Bo Van Pelt, and DA Points, Sweden's Carl Pettersson and Venezuela's Jhonattan Vegas all shot 65 for 132, while American William McGirt carded a 68.
While the tournament features a bevy of players battling to make the playoffs, others were simply trying to keep their tour cards for next year.
Three-time major champion Padraig Harrington failed in that bid after missing the cut.
The Irishman was four-over par after two rounds of 72.
Harrington won British Open titles in 2007 and 2008 and the PGA Championship in 2008, but that was his last on the US Tour.
Former world number one David Duval, trying to regain his tour card after a season bedevilled by injury, also missed the cut.
South Korea's Y.E. Yang, whose exemption for winning the 2009 PGA Championship expires this week, is also in danger of losing his playing privileges, but he kept his challenge alive by making the cut -- seven shots off the lead.