T.G.
When my girls got to this point I started keeping them up a little longer in the morning and moved to 1 longer nap. If they were used to going down for a nap at 10:30 for example, we'd head to the park at 10:15, stay busy for a while and nap when we got home. If you stretch it by 10 or 15 minutes each day you should get to the point where he makes it till lunch time, eats, and then goes down for 1 longer nap for the day. Good luck!