Langer shared the overnight lead with American Mark Wiebe but birdied three of his first seven holes to jump in front on his own. David Frost of South Africa shot his third straight 68 to sit alone in second place, while Wiebe only managed a 70 to drop into third, four shots back.
Langer's only bogey came on the 14th, but he finished with two birdies on 15 and 17 to stay in control.
"That was as good as I can play," said the German veteran, who is bidding for his second Senior British Open title having won at Carnoustie in 2010. "My ball-striking was almost perfect and I played really well, apart from the mistake at the 14th."
His lone bogey came when he hit his tee shot to the back of the green, sent his approach putt long and left and missed the return.
He got it back immediately with a birdie at the long 15th, added another at the long 17th and just missed his birdie chance from 12 feet at the last.
Frost made three birdies in a row from the seventh but then made three bogies came on the 10th, 14th and the 18th, with two other birdies in between.
Three players are in joint fourth place, six shots back — home favorite Sandy Lyle (69), Australian Peter Fowler (70) and first-round leader Gene Sauers of the U.S (70).
Colin Montgomerie of Scotland also had a 69 but is tied for 13th at 2 over. Miguel Angel Martin of Spain had the day's best round of 65 but is also on 2 over.
Defending champion Fred Couples had a 68, his best round of the week, but his out of contention at 4 over.
Ireland's Mark McNulty shared fourth place overnight but quickly fell back when he dropped a stroke at each of the first four holes and another two at No. 7 and 8. He finished with a 76.
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