Mathews made Pakistan pay dearly for a dropped catch late on Thursday when Talha could not hold onto a difficult chance off his own bowling before the skipper scored.
Khan made it two in two deliveries when he trapped Rangana Herath leg before wicket. Eranga stopped the hat-trick delivery and cut loose after tea, taken at 359-8, with Perera. After the break they added a quick 69 runs.
Perera benefited from Pakistan having spent its two reviews, as he was ruled not out to an lbw appeal by Ajmal though reviews showed he was struck on the pad right in front of the stumps with the ball pitching in line.
Prasanna Jayawardene added seven to his overnight score before he was caught at fine leg when he pulled Talha in the sixth over. But that was the only success before lunch for Pakistan.
