The Rangers forward was brought off after a 57th minutebooking and Montenegro made it 2-0 two minutes later with their first significant attack of the second half.
Emilio Izaguirre slotted home his first Celtic goal before the break, then Saints' Danny Grainger was sent off in the 87th minute for a second booking.
The Welshman was also involved as Terry received his marching orders in the 67th minute, receiving his second booking after a late challenge on the pacy 20-year-old.