A DC10 FLC DSNDED BELOW THE ASSIGNED ALT NEAR IND.

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CAPT FLYING ACFT AND WENT 300 FT BELOW ASSIGNED ALT IN DSCNT FROM 11000 FT TO 10000 FT. WENT TO 9700 FT THEN QUICKLY CORRECTED BACK TO 10000 FT. WE WERE IN VISUAL CONTACT WITH THE AIRFIELD AND FO AND SO WERE DISTR MOMENTARILY LOOKING FOR THE RACE TRACK. THIS WAS THE SECOND LEG OF THE TRIP THAT HAD A SHOW TIME OF XA10. WE WERE FATIGUED DUE TO THE INABILITY TO GET PROPER SLEEP PRIOR TO THE TRIP. ALSO; WHENEVER YOU HAVE TO FLY THROUGH SUNRISE IT IS MORE FATIGUING. WE SHOULD NOT HAVE TO FLY MORNING OUT AND BACK TRIPS. CONFUSION OCCURRED OVER ALT DUE TO FATIGUE AND VISUAL CONTACT WITH AIRFIELD. WE SEEMED TO BE VERY HIGH AND DUE TO THE FATIGUE; I CONFUSED MY MENTAL PREPARATION FOR A VISUAL APCH WITH WHAT WE WERE CLRED FOR. IN AN EFFORT TO STAY MENTALLY ALERT; THE FO AND SO WERE LOOKING AROUND OUTSIDE THE ACFT AND MISSED MY NOT LEVELING AT 10000 FT TILL JUST AS WE PASSED THROUGH THE ALT. CORRECTIVE ACTIONS: 1) BE MORE ATTENTIVE DURING ALT CAPTURE. 2) TRY TO KEEP CREW MORE FOCUSED INSIDE THE ACFT ON DSCNT. 3) TRY TO MAKE CREW SCHEDULING AWARE OF THE EFFECT OF THIS TYPE OF SCHEDULING ON CREW PERFORMANCE.