Merrett kicked five of his goals in a staggering first quarter display - and missed a sixth after the siren - to pave the way for the 19.18 (132) to 5.10 (40) victory.
It ended a three-game losing streak for the Lions and moved them to a 3-5 record ahead of a trip south to play North Melbourne next Sunday.
After Merrett's early onslaught, the Giants battled hard in the second quarter but fell away after half-time, kicking just two goals and conceding nine on a hot Brisbane afternoon.
Merrett was moved from his usual full-back post this season by coach Michael Voss and repaid the faith, racking up 23 disposals and 12 marks in his day out.
His first quarter was sublime, snapping his first goal from a pack, then leading onto precise passes from captain Jonathan Brown (twice), Simon Black and Jed Adcock and finishing set shots from all angles.
Brown had a huge day himself, running Giants' counterpart Phil Davis ragged over the four quarters.
Short of goals in his five games this season, Brown ran tirelessly and worked his way into some prime form, taking 16 marks and kicking five goals.
Although the clearances were dead even at 33, the Lions midfield got on top in the contested possessions (141-116) and spread much quicker than their younger opponents, who rested early season finds Thomas Bugg, Dylan Shiel and Devon Smith.
Tom Rockliff (36 disposals and three goals), Daniel Rich (26), Jack Redden (26) and Simon Black (25) worked hard on both the inside and outside as they ran away in the final quarter.
It was a glum day for former Lions favourite Luke Power who returned to the Gabba for the first time since playing the last of his 282 games for the club last August.
Power, cheered by all of the 16,049 fans when he ran on, had 16 disposals.
BRISBANE LIONS 7.3 10.9 13.14 19.18 (132)
GREATER WESTERN SYDNEY 1.2 3.5 4.5 5.10 (40)
GOALS
Brisbane Lions: Merrett 7, Brown 5, Rockliff 3, Karnezis 2, Rich, Zorko
Greater Western Sydney: Wilson, Giles, Phillips, Scully, Tyson
BEST
Brisbane Lions: Merrett, Brown, Rockliff, Black, Rich, Hanley
Greater Western Sydney: Palmer, Ward, Giles, Coniglio
INJURIES
Brisbane Lions: Nil
Greater Western Sydney: Jacob Townsend (calf) replaced in selected side by Nathan Wilson
SUBSTITUTES
Brisbane Lions: Jared Polec replaced Joel Patfull in the fourth quarter
Greater Western Sydney: Matthew Buntine replaced Adam Tomlinson at half-time
Reports: Nil
Umpires: McBurney, Ritchie, Armstrong
Official crowd:16,049 at the Gabba
The views in this article are those of the author and not necessarily those of the AFL or its clubs
