Adam Forshaw 's early strike gave Uwe Rosler's charges the advantage but the Bhoys hit back through new arrival Amido Balde, with youngster Callum McGregor grabbing the winner
Adam Forshaw 's early strike gave Uwe Rosler's charges the advantage but Celtic hit back before the break through new arrival Amido Balde, with youngster Callum McGregor netting the second-half winner.
Brentford, who lost in the League One play-off final to Yeovil last season, took a surprise lead after 10 minutes as former Everton youngster Forshaw headed home from close range.
Martin Fillo, on loan from Czech club Mlada Boleslav for the hosts, saw appeals for a penalty waved away soon after but it was Celtic who struck next.
Tony Watt played the ball into newcomer Balde and the Portuguese muscled past his man before slotting past Jack Bonham.
The SPL outfit almost took the lead just two minutes before half-time but Balde and Watt both struck the bar in quick succession.
Neil Lennon's side stepped up the pressure after the break and McGregor soon curled an excellent strike into the bottom corner to put the visitors ahead after 57 minutes.
Brentford rallied late on but when Forshaw's ambitious long-range shot flew just over, it signalled the end of their hopes.
The sizeable travelling support invaded the pitch at the full-time whistle and remained there even after the sprinklers had been turned on.