DHC-8; ON VISUAL APCH PHL; TURNED FINAL FOR WRONG RWY.

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I WAS PIC AND PF OF FLT ABCD TO PHL. CONDITIONS WERE VFR AND LIGHT WINDS. PHYSIOLOGICALLY; I WAS FATIGUED; STRESSED AND HAD A MILD HEADACHE. FLT ABCD WAS OUR 5TH LEG OF THE DAY UNDER THE CTL OF RUDE PHL ATC. OUR DUTY DAY HAD BEGAN 7 HRS 45 MINS EARLIER AT XA45 IN HPN WITH A STRESSFUL DRIVE TO THE ARPT AND HARASSMENT BY SECURITY. ABOUT XH20; OUR FLT WAS CLRED VISUAL APCH TO RWY 35 IN PHL. APCH ASKED US FOR A L S-TURN FOR SPACING WITH AN ACR Y AIRBUS ON APCH FOR RWY 27R. WE COMPLIED AND WERE INSTRUCTED TO CONTACT TWR. WHEN WE CHKED IN; TWR ASKED IF WE WOULD PREFER TO GO TO RWY 27L. WE ACCEPTED HIS OFFER AND TURNED R TO SET UP FOR A BASE ENTRY TO RWY 27L. ONCE I HAD MADE THE TURN; I SET UP TO FOLLOW THE AIRBUS (ON APCH TO RWY 27R). AS I ROLLED OUT ON FINAL; I HEARD ACR Y CALL TWR AND ASK WHAT HE SHOULD DO BECAUSE A DASH 8 JUST CUT IN FRONT OF HIM FOR RWY 27R. AS SOON AS I HEARD THAT; I REALIZED MY MISTAKE AND INITIATED A TURN TO REINTERCEPT THE RWY 27L FINAL. I BELIEVE MY ALT AT THAT POINT WAS STILL ABOUT 600 FT BECAUSE WE HADN'T FINISHED THE CHKLIST ITEM OF FLAPS 35 DEGS WHICH WE NORMALLY DO AT 500 FT. DURING MY TURN TO RWY 27L; TWR RESTATED CLRNC TO LAND ON RWY 27L. ONCE CLRING THE RWY; TWR ASKED IF WE HAD JUST OVERSHOT FINAL FOR RWY 27L AND NOT WANTING TO 'OPEN A CAN OF WORMS;' WE SAID 'YES.' NOT WANTING TO MAKE EXCUSES; BUT DRAWING FROM MY PERCEPTIONS OF CAUSAL FACTORS: FATIGUE; STRESS; AND HEADACHE; AND SOME SLIGHT UNFAMILIARITY WITH THAT TYPE OF APCH (IT WAS MY FIRST TO CIRCLE FOR VISUAL TO RWY 27L). BOTH THE FO AND I THOUGHT WE WERE DOING EVERYTHING CORRECTLY. I DO NOT BELIEVE MY LAST MIN MANEUVER WAS DANGEROUS OR UNWARRANTED; AS I HAD BOTH AIRSPD AND ALT. IN HINDSIGHT; I REMEMBER THINKING WHAT POOR ATTITUDES THE CTLRS HAD WHEN WE QUERIED THEM AND HOW 'SHORT' AND 'CONDESCENDING' THEY WERE WITH US. AGAIN; WE LANDED SAFELY ON RWY 27L AND ACR Z ON RWY 27R. TYPICALLY; WHEN SIMULTANEOUS APCHS TO PARALLEL RWYS ARE INVOLVED; ATC WILL BE ABSOLUTELY CLR BY SAYING 'YOU ARE CLRED FOR RWY 27L; YOU HAVE TFC ON RWY 27R....' I DO NOT REMEMBER HEARING THAT.