What was different with Castijello when fighting Vargas and Sturm?

I was watching Fernando Vargas vs. Javier Castijello again today and was wondering to myself what the difference was in Castijello between his fight with Vargas and then his fight against Felix Sturm. At this point in their careers, I believe that Sturm is the more dangerous opponent as far as their abilities go. However, Javier was able to stop Sturm in their first fight. I didn't get to see the 2nd (if someone could help me out with that, I'd appreciate it). Anyhow, I was curious of what those of you who saw these fights thought about Castijello. I mean, he was a few years older fighting Sturm, but he looked better than in the Vargas fight, where he was already an older fighter.