Van der Merwe's score helped Glasgow into a 10-0 lead at half-time, with British & Irish Lions pair Sean Maitland and Stuart Hogg coming off the bench in the second period to secure victory.
And Warriors coach Townsend wasn't afraid to play up the importance of the Canadian to Glasgow's hopes of progressing further in the competition.
"It illustrated just what a great finisher he is and how tough it is to put him down," said Townsend of van der Merwe's first half score. "So many of his tries for us have been important ones and that was also the case at Connacht.
"But DTH has proved to be a big-game player and we will need more of that from him in Dublin. We know nothing other than our best will be good enough if we want to create history and make our first PRO12 final.
"But we are going to Dublin to win and become the first Glasgow team to make the final."
The victory was Glasgow's first at Connacht since 2007, and gives the Scottish side some welcome momentum going into their play-off tie.
"They have been a bit of a bogey team for Glasgow and to get the win there and preserve our momentum going into the play-off semis is a fantastic boost," added Townsend.
"Hopefully we can enjoy a good solid week in training and make sure we make the trip back to Ireland fully focused and ready to deliver the quality of performance that will be required to beat Leinster at the RDS."
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