Cusiter - a British & Irish Lion in 2005 - spent five years at the GUINNESS PRO12 outfit, making 17 appearances last season as Glasgow reached their first ever final in the competition.
Pyrgos and Niko Matawalu were each nipping at the heels of the Scotland international and it is the same duo fighting for a starting berth this season.
And while he is eager to add to his 12 caps in next month's autumn internationals, the 25-year-old knows he cannot lose focus on the GUINNESS PRO12 - as it could mean losing that starting role.
"With Cus going last year it has given us an opportunity, I suppose - there is one less guy around - but Niko is a top player and he played well at the weekend," said Pyrgos.
"There is great competition and I think that is good in our squad. If you're not performing then you're not going to play. Hopefully I'm involved this weekend and I can put a marker down."
And while Pyrgos and Matawalu do battle at scrum-half, there is a similar battle going on outside them at No.10.
Finn Russell shone in last season's run to the final but fellow Scotland international Duncan Weir appears to have grabbed hold of the role so far in this GUINNESS PRO12 campaign.
Throw into the mix utility back Peter Horne, who started the season's first two games at fly-half, and competition is rife.
"From the outside it maybe seems like it swaps around a lot but in training you are playing with them every day," added Pyrgos. "It is quite comfortable and we have got a lot of guys who are comfortable in that position.
"Whoever Gregor (Townsend) picks, we get on well, we try and gel, we work on it through the week and it seems to go well.
"It is the same for them, really - there is a lot of competition in their position and they will be battling hard to try and start at the weekend."
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