Barr shot a 69 that left the Australian at 11-under 202 for the $250,000 tournament, part of the Asian PGA Tour. Montgomerie and Jason Knutzon (69) of the United States were at 205.
Montgomerie twice finished second on the European tour this year and is trying to keep alive a streak in which he has won at least one title the last 14 years.
'My game plan now is to go out tomorrow and score a 66 and win the tournament,' the Scotsman said.
Barr had a 66 and 67 in the first two rounds and led by two strokes entering Saturday.
'My goal tomorrow will be to keep to myself and watch my own game,' he said. 'I won't worry about what the others are doing.'
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