The 36-year-old fly-half was passed fit to play only 90 minutes before the match, after which Smith revealed talks have already started with a view to Catt playing on next season.
"We have to manage him carefully - Catty has only had 40 to 50 minutes training this week," said Smith.
"It wasn't a terrific performance, but at the end he was still making the plays and retrieving situations.
"If you knew how bad his back was you would excuse him shanking a couple of kicks.
"He's a Ferrari. He's got a hell of a lot of miles on the clock but he's a competitor."
Irish, who have collected 14 out of a possible 15 points by winning their three opening matches in Pool One, are expecting a hot reception in the return match in France next weekend - after full-back Peter Hewat's injury-time penalty denied Perpignan even a losing bonus point.
Irish had earlier scored through Bob Casey and a penalty try, while Adrien Plante's touchdown had briefly put the visitors in control.