David Goodwillie had given the hosts hope after deflected goals from Anthony Stokes and Mark Wilson put Celtic in command but Daniel Majstorovic's diving header sealed the Bhoys' win.
"I don't think we turned up in the first half. I don't think we played anything near what we have been doing recently," Houston said.
"For some reason we didn't come out the traps and if you give a good Celtic side a two-goal start you are always going to be up against it.
"When your better players can't pass the ball to each other, they are either nervous or Celtic put them under pressure. I felt Celtic put us under real pressure when we had possession.
"Rather than criticise my players, and yes they should have done better, I give credit to Celtic because they did the job properly."
Source: PA
Source: PA