Cusack had not been included in a squad since a trip to Rodney Parade in February 2014 and his appearance on Friday was his second GUINNESS PRO12 appearances in the last two seasons.
Injury and illness had combined to keep the 30-year-old out but he packed down to great effect at Scotstoun, as the Warriors bounced back from their 1872 Cup defeat the week before.
He was not the only returnee - fellow front-row Jerry Yanuyanutawa made his first appearance for three months - and Townsend admits his sudden strength in depth leaves him in an enviable position.
"All credit to Mike Cusack to come into a game like that when there's a lot of scrums and a lot of work to do into the wind," said Townsend.
"He was great. Yes, he's got to work hard to get fitter and get match fitness, but we're really pleased for him.
"It is a good position to be in when the props are challenging each other.
"Jerry was fantastic, he's not played for us since October, so he's had to work really hard and he's had a couple of injuries.
"I thought the way that both props played in the first half sent a message to the two props that came off the bench.
"I could tell Ryan Grant was fired up, with great carries and tackles, and Euan Murray was the same, really worked hard."
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