Too easy to be dominated by either a better ace or a pair higher than 5's
I think you overestimate how easy it is to have those hands. Yes, he
could have a dominating ace, or a dominating pair, but he could also have any king, any two cards higher 9 or higher, or worse aces.
With his stack size, number of players, position, what range of hands do you put him on?
If he's pushing
top 40%, I'm a coinflip with a 2:1 overlay. If you think he's tigher, top 25% for instance, I'm a 1:1.4 dog. If you think he's top 15%, I'm a 1:2 dog, which means the play is even +/1chipEV (but I assume tournament -EV?), but it's awfully generous to give him that range of hands, isn't it?