Intermittent Hard To Start

I have a 1996 Escort Wagon with 52K miles.Usually it starts right up with no problem.Occasionally,it will be hard to start.It turns over OK but I will have to try 2-3 times of cranking for several seconds before it will start.This can happen first thing in the morning or even after driving it for a while.I've had both O2 sensors replaced and had the fuel injectors cleaned within the last 2 months.It runs perfect once it starts so I have no idea what to start checking.