Having shared the overnight lead with American Gary Rusnak, the 2010 European Ryder Cup captain claimed the outright advantage with a birdie on the first, but then gave that shot back with a bogey on the par-3 third.
He then birdied the fifth, 10th and 12th holes, but dropped a shot on the 15th before holing an eight-foot birdie on the last for a seven under total of 137.
In contrast, Rusnak found the trees on the closing hole en route to a double bogey six, meaning he slipped back to one under par, leaving fellow American Mike Cunning, who posted a round of 68, as Montgomerie's nearest challenger on three under par.
The eight-time European No 1 was happy with his round. "It was job done today," said the 51-year old. "It was important to keep moving in the right direction, which I've done."
As well as aiming to become only the second player after Carl Mason to defend the title, Montgomerie is also trying to beat Mason's record as the quickest player to win four times on the European Senior Tour.
Mason achieved the feat in 11 appearances. In contrast, Montgomerie is playing in his ninth event, and victory would also further extend his commanding cushion at the top of the Senior Tour Order of Merit.
"If I am under par I should be safe," he said. " But there are a lot of good challengers who can shoot a 66 so you have to be careful. I'll watch the leaderboards and play conservatively to a point, but at the same time when it is time to attack I will do so."