The 56-year-old Langer, who won his first European Tour event, the Dunlop Masters, 45 miles from here at St Pierre in 1980, fired a stunning 66 to add to his 65 of Thursday to go to 131 - 11 under par.
He was an early finisher and that put him seven strokes clear of England's Chris Williams, who produced a 70 for a 138 aggregate.
Then Montgomerie, seeking to complete the grand slam after victories in the US Senior Open and Senior PGA in the United States.
The Scot was one-over par on 71 and began poorly with two bogeys which threatened to derail his challenge before he stormed up the leaderboard with an amazing run of six birdies in seven holes.
His approach play and putting was immaculate on this fiery course and a pivotal moment in his round came when he chipped in at the eighth. He went out in a spectacular 31 which equalled Langer's outward half score on Thursday.
Another birdie followed on the 13th but he dropped a stroke at 16 before finishing with a par and birdie.
His 66 - the same as Langer - put him on 138, tied with Chris Williams, and seven behind the German.
"I felt good with my game today; I just took off from the third and there was no looking back,"said the 51-year-old Scot.
Tom Watson closed with an eagle 3, also for 66, and a 140 total.
Ross Drummond, the 57-year-old former Tour player from Paisley, will be challenging this weekend for a major slice of the prize money after sweeping into the top 15 with a steady level-par 71 for 143 aggregate. Two birdies in the first four holes put him on the right track and he compiled halves of 35 and 36.
"I am pleased with the way I hit the ball today. It was a steady round on a course that can cause many problems,"said Prestwick-based Drummond.
Alastair Webster comfortably made the cut after a creditable 72 - an improvement by three strokes on his opening round - gave him a 36-hole total of 147.
Three birdies in four holes at the start of the homeward half was a blow but in a mixed round he birdied three of the four short holes as he compiled halves of 35 and 37.
Sandy Lyle's campaign came to a disappointing end, the former Open and Masters chamnpion finishing with a double-bogey 7 for an 82 and 158.Gordon Brand junior, with consecutive bogeys, joined him.
Kenny Hutton,the ex-Downfield professional who carded a level-par 71 on Thursday, scraped through on the mark of 149 despite losing his way yesterday. He opened with a double-bogey 6 and collected three bogeys on his way to the turn in 39, coming home also in 39, a double-bogey 7 on the 13th and three bogeys on the last five holes almost costing him his place in the weekend..
Andrew Oldcorn also made the cut, adding a 78 to his opening 69.
Among those to fall by the wayside was the defending champion Mark Wiebe (153).