Merewether has knocked The Waratahs out of the NHRU finals.
The Tahs wasted little time getting on the board, Tim Riley had too much pace for the Greens.
Merewether hit back a few minutes later, as Blake Creighton dived over.
The Greens pushed further in front when skipper Gareth Ernst found space near the posts.
A penalty to the Tahs Adrian Curry reduced the margin.
Returning from the bin, Alex Robson combined with Riley to cut the margin to one, but Merewether would hold on after the break.