'I am delighted, especially as I won in Asia last year,' said Montgomerie. 'I obviously like it here, the crowd seems to like me here and I like them and it seems to work very well. I look forward to coming back.'
Montgomerie stood three shots behind Barr to start the final round at Macau Golf & Country Club, but posted a round of 68 to grab a share of the lead and force the playoff.
The veteran Scot continued his streak of winning at least one tournament every year since 1989.
'Now I go to the Volvo Masters with renewed confidence and we'll see what happens but I have kept the streak alive,' said Montgomerie. 'I am leaving it later and later, it's getting difficult. I am leaving it too late. October is too late, I would rather win in January.'
India's Arjun Atwal finished two strokes back alone in third place at 9-under-par 275.
Kevin Na, Wei-lan Lu and Jason Knutzon shared fourth place at 7-under-par 277.