1 nap or 2?

Whew, today has been a long day. Campbell has been sleeping less and less during his morning naps, and so I thought we'd try this week going to 1 nap a day. First couple of days were fine, partly because we were with my sister and nephew. It's always better to have a playmate! But today has been the breaker. I put him down at 1:00, and he slept an hour, cried, went back to sleep for 30 more minutes, then was up for good. OK, I'm all for this 1 nap a day stuff, but an hour and a half is just not enough. So I made him stay in his bed for the full two hours. I got him up and he was pretty good for about 15 minutes. Then it was evident that he was still very tired. And with church tonight pushing our bedtime back to 8:30 at least, this was not good. So now, he's back in his bed, and quiet for the moment. I haven't been brave enough to check the video monitor yet.
So, any thoughts on when to go to 1 nap? I don't know if he's really not ready or if maybe it takes a few days to devolp a new sleeping pattern. Any thoughts? I'll take any and all ideas.