Open champion Collin Morikawa leads the way with five under par alongside Joel Dahmen after a stunning second-round 66, with defending US Open champion Jon Rahm and four-time major winner Rory McIlroy one shot behind.
Masters champion Scottie Scheffler was in the group another shot back, with England’s Matt Fitzpatrick three under the pace on two under.
McIlroy was in danger of falling out of favor when he covered the front nine in 36, the world number three needing three attempts to sneak onto the green from a thick rough on the third, before breaking through from 23ft to save a double bogey.
But after dropping a shot on the 10th, McIlroy recovered shots on the 12th, 14th and 17th to stay firmly in the hunt for his fifth major title and first since the 2014 US PGA.
Scheffler was twice after seven holes but then birdied on the eighth and 13th, drilled 55 yards for an eagle on the par five 14th and landed another shot on the 16th in his bid for an incredible fifth victory in 2022 .
“I just stayed very patient,” Scheffler said. “I was hitting him well most of the day. Two stupid bogeys early in the round, but other than that I was hitting him really well.
“If a few more putts had fallen against (running) around the rim, it would have been a really special day. But three under was a good score for me, especially being two out of six.”
Speaking of his eagle on the 14th, Scheffler added: “I hit a good shot in the middle and then I had a fun kind of lie where he was sitting on a downhill slope and that made that shot into the green a lot more difficult.
“I caught him with a thin hair and hit the tree. Luckily he didn’t hit the tree and came back, he just fell in front of him. I had a good lie and I hit a good chip and he went in.”
Fitzpatrick recovered from a bogeys hat-trick to play his final five holes at two under par as he seeks a Brookline double following his American amateur triumph here in 2013.
“I played really, really well,” said Fitzpatrick, who finished fifth in the US PGA last month. “Three of my four bogeys were three putts, so that sums up the day.
“I felt like I hit the ball tee to green really, really well. I think I hit a chip shot all day, so that sums up how much I felt like I had hit him. I feel like I left a few there, which is pretty rare at the US Open, but it’s a positive going into the weekend.”