Neil Lennon's side lost for the third successive time at Hampden as the highly-unfancied Buddies won 3-2 to scupper any hopes of a Hoops treble.
The Wales right-back admitted the players were solely to blame for the Buddies bruising but is confident they will get back on track against Kilmarnock and continue on their quest to retain their Scottish Premier League title.
"I think everyone is a bit down but the game tonight is a good opportunity to put it behind us so that's what the boys are looking to do," he said.
"I don't think the manager can take the blame for Sunday.
"As players, we know we didn't play anywhere near as well as we can.
"I think we have shown this season that we can perform in big games but we didn't perform on the day and St Mirren deserved it in the end.
"Everyone steps their game up when they play us, St Mirren did that, so we have got to be on our toes.
"We know Kilmarnock can cause us problems so we have to nullify them and get the three points."
Kilmarnock signed midfielder Sammy Clingan yesterday but the Northern Ireland international will not face the side of his friend and former Nottingham Forest team-mate Lennon as he is working on his fitness.
Clingan said: "I've known Lenny for years. I was at Nottingham Forest when he signed in 2007 and we got on really well.
"I came up to Glasgow with him for a few games at Celtic Park. We went to the Champions League game against AC Milan and I stayed in his house in the city. I also stayed with him at times in Nottingham.
"I haven't seen him for a few years now so it will be good to catch up. We always got on really well."