LGT TAKES WRONG TXWY; CAUSES DELAY FOR OUTBOUND ACFT.

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AFTER LNDG AT LAS AND CONTACT WITH GND CTL; WAS TOLD TO TAXI TO THE GATE VIA TXWY A4 RAMP TO THE GATE. AS WE WERE APCHING THE RAMP AREA; GND CTL CHANGED OUR CLRNC TO A4 HOTEL TO THE GATE; SO AS TO ALLOW ANOTHER ACR (B-737) TO TAXI OUTBOUND. THE CAPT SEEMED TO BE TAXIING A LITTLE TOO FAST AND MISSED THE A4 TXWY; SO HE JUST CONTINUED VIA THE RAMP TO THE GATE. AS WE PASSED IN FRONT OF THE AWAITING OUTBOUND ACFT (WHICH WAS NOT MOVING); GND CTL RESTATED OUR TAXI INSTRUCTIONS AND INFORMED US THAT WE WERE ON THE WRONG TXWY. ALSO; THE OTHER PLT MADE A COMMENT TO GND CTL ABOUT OUR POS. BEFORE I COULD PICK UP THE MIKE AND RESPOND TO GND CTL; WE HAD ALREADY TAXIED IN FRONT OF THE OUTBOUND ACFT. WE APOLOGIZED FOR THE ERROR AND CONTINUED TO THE GATE. NOT MUCH ELSE WAS SAID ON THE RADIO. I FEEL THIS COULD HAVE BEEN A DANGEROUS SIT IF THE OTHER ACFT WAS MOVING AND DID NOT SEE US AS HE CONTINUED TO TAXI OUTBOUND. LUCKILY; HE REMAINED STOPPED UNTIL AFTER WE HAD PASSED. I FEEL THIS SIT COULD HAVE BEEN AVOIDED IF THE CAPT WAS NOT SO ANXIOUS TO GET TO THE GATE AND TAXIED A LITTLE SLOWER TO ALLOW FOR ANY CHANGE IN TAXI INSTRUCTIONS.