But despite their dominance in the opening 40 minutes Glasgow's nerves in the second period were clear to see with Edinburgh going over through Piers Francis.
Glasgow made the brighter start and got their rewards as early as the sixth minute when van der Merwe crossed in the corner.
The winger was the grateful receiver of Peter Murchie's well-timed pass and he went over unopposed.
Pete Horne was wayward with the conversion but eight minutes later it was the same left corner that saw Glasgow's second try, this time courtesy of Harley.
The back row was in acres of space after some relentless Warriors pressure to touch down and extend the hosts' lead to ten points - Horne's boot again letting him down from a tight angle.
Glasgow's superiority was further highlighted on 25 minutes when Van der Merwe went in for his second try - again on the left-hand side that had brought so much early joy for the Warriors.
This time the flying wing had Nikola Matawalu to thank for a delightfully weighted kick and Horne also found his range with the boot, converting his first of the evening.
Greig Laidlaw got Edinburgh off the mark with a penalty just after the half-hour and it seemed to galvanise the visitors into action.
The Gunners spent the rest of the half camped in Glasgow territory but couldn't make it count and went into the half-time break 17-3 adrift.
Laidlaw's second penalty of the evening five minutes after the restart reduced Edinburgh's arrears still further before Francis crossed for the visitors.
An incisive break from Matt Scott found the fly-half who bundled his way over the line on 49 minutes - Laidlaw missed the conversion from out wide.
Duncan Weir slotted over a penalty for the Warriors to give them a bit of breathing space at 20-11, but Laidlaw kept his side in it with another three-pointer.
Not be outdone replacement Weir notched his second penalty of the evening and despite some late pressure from the visitors the Warriors held on and put one hand on the 1872 Cup.
|Glasgow Warriors Score Card|
|DTH van der Merwe||2||10|
|Edinburgh Rugby Score Card|