In the wind and rain neither side could get a grip on the game, but Glasgow's replacements told as Scotland No.8 Adam Ashe piled over with nine minutes left to play.
Duncan Weir added a conversion and penalty to cement the 13-6 win - the reigning champions' third GUINNESS PRO12 success in a row - and Townsend believes it was a night for grit rather than grace.
"I'm delighted because we were trailing for a long time," Townsend said.
"Fair play to Treviso, they came with a very specific game plan, looked after the ball very well in the first half, we didn't get to see it that often.
"I think the weather conditions and the opposition were the factors in how we maybe didn't play as well as we'd set out to.
"It was a night for ball carries and defending, and players really stepped up there. It wasn't a night for those passes across the field and offloads, but I thought the pack played very well.
"I thought the subs, both backs and forwards, made a big impact. It's quite tough when you come into a game when it's cold and wet but they did very well."
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