Pendleton wasn't durable enough or strong enough to beat Mancini. Ray might get stunned a few times, but he would mug Pendleton.
I think Mancini breaks him down in a great, great fight. Pendleton was a good puncher and Mancini may have to ride out some hard moments, perhaps even a knockdown, but I think he doesn't give Pendleton much space and works the body on the inside. Pendleton's 1-2 and uppercuts present issues for Mancini, but not as many issues as Mancini's aggression, head-movement and combinations would pose for Pendleton's non-existent defence. Paez and Ruelas (maybe others too, I'm gonna watch a lot more Pendleton soon) showed that pressure fighters were pretty bad for him IMO. Pendleton had a pretty good chin though, I don't think it's out of the question that he sees the end.
When I think of this fight, hard not to reflect on the Bramble fights. Pendleton was rugged, determined and quick, a lot like Bramble.
He was a lot less durable than Bramble. If Rafael Ruelas can soundly outfight Pendleton, i see no reason why Mancini couldn't.