The result means that the Warriors have put themselves on the threshold of claiming a RaboDirect PRO12 home semi-final for the first time. Townsend's team only have to beat Zebre at Scotstoun next Saturday to make that dream come true.
The victory was the Warriors' seventh win on the trot, and Townsend said that Seymour had established himself as a critical figure in that run even before his haul of scores last night.
"He has been in great form all season," said the coach. That's why he got in the Scotland team last year. In the last few weeks he has been outstanding. He had a great game against Ulster and he scored a crucial try against Ospreys. It's great to see him playing with so much pace and power and making great decisions. He scored two tries here last season as well, so it has been a happy place for him."
However, Townsend was just as pleased with the all-round effort of his players in difficult conditions in the north of Italy. "That has to be one of the best performances of the season," he said. "We knew it was going to be a really tough game here because Treviso had a lot to play for and there was a lot of emotion there with a number of their players leaving.
"I don't know where that second-half performance came from in these conditions. There were some outstanding tries. We probably performed above expectations given the side Treviso selected and the nature of the game in the first half.
"When we came out in the second half it was pouring with rain and we really didn't think there were four tries in the game. The handling and support play were outstanding."
In last night's other significant match, Leinster stretched their lead at the top of the table with a 22-20 win at Ulster. Were Munster to take nothing from their meeting with Edinburgh today, Glasgow's home semi-final would be guaranteed.