London Irish (8) 24
London Irish centre Delon Armitage takes on the Perpignan defence
Tries: Casey, penalty
Pens: Hewat 4
Perpignan (9) 16
Cons: Porical 3
London Irish went five points clear at the top of Heineken Cup Pool One after fighting back to beat Perpignan.
Exiles second row Bob Casey scored the opening try of the match but three Jerome Porical penalties gave Perpignan a 9-8 half-time lead.
Adrien Plante crossed after 47 minutes but that was the visitors' final score.
A Peter Hewat penalty and a penalty try put Irish back in front and two late Hewat penalties ensured the hosts denied Perpignan a losing bonus point.
Both London Irish tries came when Perpignan were a man down after yellow cards.
The French lost three men to the bin in total, with London Irish's David Paice also getting a yellow card from referee Malcolm Changleng.
London Irish director of rugby Brian Smith on 36-year-old Mike Catt:
"We have to manage him carefully - Catty has only had 40 to 50 minutes training this week.
"This morning we didn't know if he would play; at lunchtime he said he would give it a spin, and by five o'clock he'd played 80 minutes.
"It wasn't a terrific performance, but at the end he was still making the plays and retrieving situations. He's a Ferrari. He's got a hell of a lot of miles on the clock but he's a competitor."
Perpignan's England prop Perry Freshwater on their three yellow cards:
"Sometimes the boys can lose their heads - and some of them do. I don't want to take the fire out of the bellies of anyone, but we need to be less fiery.
"The boys, the coaches, everyone is up in arms as they often are - but it isn't about the ref. We need to go away and look at ourselves.
"You get a lot of frustration, because they can't talk to the ref and don't know why things happen - but we just have to learn to live with it. We've got to learn to react to different referees in different competitions."
London Irish: Hewat; De Vedia, D Armitage, Mapusua, Tagicakibau; Catt, Richards; D Murphy, Paice, Skuse, Kennedy, Casey, Roche, Danaher, Leguizamon.
Replacements: Lea'aetoa, Mackie, Hudson, P Murphy, S Armitage, Hodgson, Pedro Tiesi.
Perpignan: Porical; Manas, Marty, Grandclaude, Plante; Hume, Durand; Freshwater, Tincu, Bozzi, Alvarez, Hines, Vaki, Chouly, Tuilagi.
Replacements: Guirado, Pulu, Mas, Olibeau, Mele, Rosalen, Britz.
Referee: Malcolm Changleng (Scotland)