A B757-200 pilot deviated below his cleared altitude in descent when he lost situational awareness. Fatigue was cited as a factor.

Narrative

Cleared FLIPR ONE RNAV ARRIVAL into MIA. On descent became distracted and descended below 10;000 FT. First Officer called out 'altitude' as we went through 10;000 FT. I immediately added power and smoothly raised the nose to climb back to 10;000 FT. Aircraft descended approximately 400 FT below 10;000 FT. Aircraft was stable at 250 KTS and 10;000 FT well prior to crossing FLIPR. ATC made no mention of deviation. Autopilot was off during occurrence. I have no recollection of disengaging it or if it disengaged itself. I had assumed it was on at the time of occurrence. I believe fatigue was a factor in my loss of situational awareness. Previous night's flight was 3.5 hours delayed; arriving at an international destination well after midnight local. Approximately one hour later; as we were checking into hotel; crew scheduling calls to inform us that our departure later that day is pushed back 10 minutes to make us legal for minimum layover. Got to sleep shortly thereafter and woke up about five hours later. Departure was in mid afternoon five hours after wake up to MIA. Deviating around build-ups the whole flight to MIA. Continuous light chop most of the enroute. Weather approaching MIA cleared and the descent was in VMC with twenty plus miles visibility. Obviously let my guard down mentally and physically when the weather improved on descent. My habit pattern is to fly the autopilot down to the terminal area then hand fly approach. As I stated; I do not remember the autopilot disengagement. This is a serious wake up call as to the insidious affects of fatigue. I felt slightly tired but still felt I had my 'A' game on which was definitely not the case.