It left Montgomerie in second place after the round, but the only man ahead of him, the South African Retief Goosen, had a chance to follow up his morning 64 as tournament officials tried to make up for lost time by sending out half the field to play their second rounds before nightfall.
Two weeks ago Montgomerie was beaten at the US Open by Ernie Els, after bogeying the penultimate hole, but looking ahead to the Open at Royal Troon he said: "It's great to be going into this stretch playing possibly the best I've ever done.
"I am very confident in what I am doing. I can hit a poor shot and not worry because I know the next one or the next putt will be good."
On the National course where he missed the half-way cut last year, Montgomerie's one error came when he took three putts at the 15th.
Happy though he was with his own day's work, it was then discovered he had made another mistake and it led to the defending champion, Robert Allenby, disqualifying himself.
Montgomerie was marking Allenby's card and put him down for a par three at the short 11th when the Australian had taken three putts.
Allenby actually shot 78, but signed for a 77 and when he realised he owned up. "I was thinking about it on the practice range and asked my caddie if the course was a par 71, but when he said it wasn't I went back to look at my card. Exactly the same thing happened here two years ago."
As a consequence Montgomerie will have only one playing partner for his second round today, the player he thinks could be the biggest danger to him.
Lee Westwood, who has impressed virtually everybody he has played with this season, opened with a 67 and Montgomerie said: "He is definitely the best young player we have on tour. He has a very, very good temperament, is long and straight and will be a great asset to the Ryder Cup team."