Russell took over with a moment of magic as his long, looping pass found the hands of van der Merwe, who had come off the bench to make his first appearance since injuring his hand last month.
He finished with aplomb and it was left for man-of-the-match Russell to break the deadlock by nailing a tricky conversion from the right-hand touchline to send Scotstoun into raptures.
"When we were behind by five points, there was some doubt in the back of my mind but the forwards were amazing to keep the ball and create the space for DTH," Russell told the Warriors' official website.
"To come back from injury like he has and to finish that move under so much pressure is just testament to how good a player he is.
"It's so fitting that he scored that try.
"When I was lining up the kick I was just thinking about how I didn't want it to go to extra time as my legs didn't have much more in them.
"I wasn't too nervous when I stepped up and was just so relieved to see it go over."
Warriors can now sit back for a little while and watch Munster and the Ospreys do battle for the right to join them at the Kingspan Stadium final on May 30.
Russell added: "I've not thought too much about (the final) as we don't know who we're playing yet.
"We know we need to play to our full potential for the 80 minutes and we're hopeful we can lift the trophy."
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