AN ACR FLC IN A B737-300 MISUNDERSTOOD A CLRNC AND PROCEEDED TOWARD THE WRONG INTXN. THE CTLR CORRECTED THEM.

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EARLY MORNING FLT FROM BUR TO SFO. BECAUSE OF THE EARLY HR WE WERE RTED TO THE MODESTO 2 ARR INSTEAD OF THE BIG SUR ARR. INTERCEPTING THE ARR FROM THE S; WE WERE CLRED DIRECT GROAN; WHICH IS ON THE MODESTO 2. I THOUGHT THE CTLR SAID DIRECT TDROW AND READ THAT BACK. TDROW IS ON THE RNAV APCH TO RWY 28R. THAT IS WHAT WE WERE EXPECTING AFTER THE MODESTO 2 SINCE IT WAS VMC. THE CAPT ALSO THOUGHT THE CTLR SAID TDROW (NOT GROAN). THIS WAS ONLY A 10-15 DEG HDG CHANGE. AFTER 5 MINS; THE CTLR (ZOA) QUERIED US AND TOLD US TO GO DIRECT GROAN. I SAID WE WERE; THEN; CONFUSED; I ASKED THE CTLR TO SPELL THE FIX. WHEN HE DID; WE UNDERSTOOD OUR ERROR. IT WAS EARLY IN THE MORNING. BOTH THE CTLR AND I PROBABLY MUMBLE AND ARE HARD TO UNDERSTAND. THE CAPT AND I WERE EXPECTING THE FMS VISUAL APCH TO SFO AND WERE SPRING LOADED TO THOSE FIXES. THE CTLR MISSED MY INCORRECT READBACK. THERE ARE 2 FIXES ON THE FMS ARR THAT SOUND LIKE GROAN (TDROW AND GAROW) ESPECIALLY EARLY IN THE MORNING. AN INITIAL SPELLING OF THE FIX BECAUSE WE WERE SOMEWHAT CONFUSED BY THE FIX ON OUR INITIAL CLRNC WOULD HAVE PREVENTED THIS DEV.