Shane Lowry added a second round of 69 to his opening 66 for a halfway total of seven under par and two-shot lead over English duo Justin Rose and Dan Brown, who both came through 36-hole final qualifiers earlier this month.
With a strong wind sending scores soaring for the later starters, Tiger Woods, Rory McIlroy, Bryson DeChambeau, Ludvig Åberg and Tommy Fleetwood all missed the cut, but home favourite Robert MacIntyre and Justin Thomas fought back from horror starts to make the weekend.
Lowry also recovered from a double bogey on the 11th with birdies on the 16th and 18th as he bids to lift the Claret Jug for a second time following his triumph at Royal Portrush in 2019.
Surprise overnight leader Brown, who had completed a flawless 65 at 9.33pm on Thursday, battled to a second round of 72, while Rose returned a superb 68 and has dropped just one shot in 36 holes.
Lowry felt he had “done the hard part” on the 11th by getting his tee shot in play, but was distracted by a cameraman on his second shot and pulled it into the gorse.
After taking a penalty drop Lowry hit his fourth shot to around 10 feet to give himself a chance to salvage a bogey, only for his original ball to be found by a spectator.
That meant it was still in play and, after a long delay while it was determined where he could best take a drop, Lowry hit his approach just short of the green and eventually completed a double-bogey six.
Former Ryder Cup player David Howell, the on-course commentator with Lowry’s group for Sky Sports, said the spectator who found the ball was “being a little sheepish” when he realised Lowry’s intentions, adding: “He’s feeling awful.”
“I hit a great provisional,” Lowry explained. “The referee asked me going down (the fairway) did I want to find my first one, and I said no. So I assumed that was OK.
“Then we get down there and somebody had found it, so apparently you have to go and identify it. I felt through that whole process of that 20 minutes of seeing where I could drop I was very calm and composed and really knew that I was doing the right thing.
“And Darren (Reynolds, his caddie) did a great job too. He kept telling me we have loads of time, we don’t need to rush this.
“To be honest, I was happy enough leaving there with a six. It wasn’t a disaster. I have felt quite calm and composed the last couple of days. I’ve felt really in my comfort zone.
“Sometimes you are in a frame of mind where you get on with it better than other times. This week in my head feels like that, where I think I’m ready to take what comes, take what’s given to me out there.
“Anything that’s thrown at me, I feel like I’m ready to take it on the chin and move on. If I give myself a chance on Sunday I know I can do it and that’s as good as a position to be in as any.”
Brown might have been expected to come back down to earth with a bump after his Thursday heroics, but the 29-year-old from Northallerton delivered an impressive sequel on his major debut.
“I’ve always been quite laid back really,” Brown said. “I think I am a bit of a realist as well.
“I know I’m not going to start getting ahead of myself and thinking, ‘Oh my God, I’m leading the Open’ or ‘I’m second in the Open’ or whatever.
“There’s still 36 holes left. I might have a good round tomorrow and then I might have a stinky round on Sunday. You just don’t know.”
Rose’s round drew high praise from six-time major winner Sir Nick Faldo, the last English winner of the Open in 1992, during a commentary stint on Sky Sports.
“Maybe the best 68 of his whole career on a day like today in this wind,” Faldo said.
Speaking about his chance to make history, Rose said: “When I won the US Open (in 2013) it was like ‘First since Tony Jacklin’ and they are nice moments when they come together, but you are never thinking of it.
“In the moment you are just trying to get the job done.”
World number one Scottie Scheffler, Billy Horschel and Dean Burmester were five shots off the lead on two under par, with Jason Day, Xander Schauffele, Patrick Cantlay and Corey Conners all one under.
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