Malcom Hubbard hit a belligerent half-century and Quentin Sampson took 3 early wickets as the Essequibo side powered past the Select XI by the huge margin of 166 runs.
Essequibo posted 273-9 in their 50 overs after contributions from Hubbard who smashed 76 off 73 deliveries.
All-rounder Ricardo Adams hit 48 while skipper Antony Adams supported with 39 and Kemol Savory 29.
Leading the bowling for Select XI was Isai Thorne with figures of 4-52. Captain Junior Sinclair also contributed by taking 3 wickets.
The GCB Select XI struggled throughout their innings and never looked like achieving their target and eventually were bowled out for 107 in 32.2 overs.
Opener Raymond Perez fought back briefly with 34 off 42 balls, which included 2 fours but he frequently lost partners as the innings never really got going.
The GCB Senior Inter-County Super50 will continue on Tuesday with Demerara facing Essequibo at GCC while defending champions, Berbice will meet the GCB Select XI at Enmore. Matches start at 09:00 hours.
Scores:
Essequibo 273-9 (50 overs)
Hubbard 76, R Adams 48, A Adams 39, Savory 29
Thorne 4-52, J Sinclair 3-40, Barnwell 2-60
GCB Select XI 107 All Out (32.2 overs)
Perez 34, Dhanai 23
Sampson 3-20, Phillips 2-10, Cadogan 2-11, A Adams 2-30