After missing a five-foot par putt at the 17th hole, the Scot made amends at the last when his slick downhill putt broke perfectly into the middle of the cup for a three-under-par 68 at Harbor Shores.
On a day when overnight co-leader Tom Watson fell four shots from the lead with a 72, Montgomerie edged within sight of his first official victory in the United States.
"Any time you're one ahead of (Langer, you're) doing something right," Montgomerie told NBC TV after posting a seven-under 206 total with one round left.
After having complimented his great European rival, Montgomerie wasted no time tweaking the German, who is renowned for playing with glacial speed.
"It's tough in many ways because he's not the quickest," said Montgomerie, who will play with Langer for a fourth consecutive day in Sunday's final round.
"You try to play your own game but you are caught up in what he's doing and the clock and all the stuff that goes on there, so it's not easy to play with him but at the same time he's a great golfer and a lovely fellow. He's just a bit slow."
Montgomerie has 31 wins on the European Tour, but his only American victory came at the unofficial 1998 World Championship match play event, which the following year became a WGC event.
Langer is not the only player within striking distance of Montgomerie at the second major of the year on the over-50s Champions Tour.
Japan's Kiyoshi Murota (70) and Americans Bart Bryant (70)and Marco Dawson (64) are two shots behind while Watson is among a group of five who trail by four.
- Sports & Recreation
- Tom Watson