At Allentown in Pennsylvania, Green shot a 6-under 64 to be equal with South Korea's Y.E. Yang and Sweden's Robert Karlsson on Friday.
The leaders are one stroke ahead of Tim O'Neal, New Zealand's Steven Alker and Thailand's Thongchai Jaidee at the Lehigh Country Club.
Green, 55, is angling for his second PGA Tour Champions title after he won the Rogers Charity Classic last year. He led the field in greens in regulation (17 of 18) on Friday.
"Very, very happy," Green said of his round. "If I can keep that sort of form up over the next couple of days, who knows?"
There are three weeks remaining in the regular season before the top 72 players advance to the Charles Schwab Cup playoffs. That increases the pressure on players like Karlsson, who entered the week 58th in the points standings.
"It hasn't shown, but (at the most recent tournament at Pebble Beach) it kind of clicked and I got especially the mental thing working a bit better, being more patient out there when things went wrong, just take it one at a time," Karlsson said.
Karlsson had seven birdies through 14 holes before taking his only bogey of the day. Yang also finished with seven birdies and a single bogey.
Alker, who sits third in the Schwab Cup points race, ended his round with back-to-back birdies. He also had a scare when his caddie, Troy Martin, apparently fainted during the round.
"I was pretty concerned about Troy, first of all," Alker said. "He just stopped, literally just started walking and then stopped and went down. He got checked out, he's doing OK, that's good news.
Tied for seventh at 4-under 66 are Michael Block, Tommy Gainey, Dicky Pride and Argentina's Ricardo Gonzalez.
Schwab Cup leader Stewart Cink shot a 1-under 69 to be tied for 30th.
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