The two-time Masters Tournament winner from Germany went into the third round tied with US Ryder Cup Captain Corey Pavin on four under par.
But while Langer - seeking a first Senior Major title after seven top ten finishes - kept his card bogey free for the first seven holes, Pavin dropped a shot at the third.
The American, playing his first Senior Major after turning 50, did pull the shot back at the sixth, and at level par for his first seven holes was alone in second place.
Another American, Mark Calcavecchia - the former Open Champion who was second at the halfway stage at St Andrews last week - had moved into third on three under with a one under par first 11 holes.
Gary Hallberg was about to set the clubhouse target at two under - the American four under for the day with one to play.
He was level with compatriots Dan Forsman, Jay Haas, John Cook and Russ Cochran as well as Wales' Ian Woosnam.
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