FLC OF LGT MADE TIMELY DSCNT FROM HIGH ALT CLB AFTER UNABLE TO PROPERLY PRESSURIZE ACFT RESULTING IN DIVERTING TO LAND.

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SO NOTED A LIGHT ON PANEL THAT INDICATED FORWARD OUTFLOW WAS CLOSING; SO HE WAS WATCHING PRESSURIZATION CAREFULLY. AT APPROX 26000; AFTER TRYING STANDBY AND MANUAL MODE; HE COULD NOT PREVENT CABIN CLB BELOW 800 FPM RATE. CABIN AT THIS TIME WAS JUST BELOW 8000. I ASKED ZLA FOR A TURN TO LAS VEGAS AND A DSCNT TO 10000. I WAS GIVEN THE TURN AND CLRED TO FL240. THE FO BEGAN THE DSCNT; EMER DSCNT CHKLIST -- SLIGHT SPD BRAKES; PWR UP SOME ON #1 AND #3 ENGS TO SUPPORT PRESSURIZATION. I EXPLAINED TO CTR THAT WE CURRENTLY DID NOT HAVE AN EMER; BUT WOULD IF UNABLE TO CONTINUE DSCNT. HE TOLD ME HE HAD TFC BLOCKING 190/200 AHEAD. I ASKED FOR A VECTOR CLR OF TFC AND HE CLBED US TO 310 DEGS HDG AND 10000 FT AT APPROX 17000 FT CABIN WAS ALMOST STABILIZED AND NEVER EXCEEDED 10000 FT AFTER 15000 ATC REQUESTED PAX ONBOARD; FUEL; ETC; AND I EXPLAINED THAT WE DID NOT HAVE AN EMER. A TIMELY DSCNT PREVENTED THAT; BUT THAT I WOULD SUPPLY THAT INFO IF NECESSARY; WE WERE BUSY CALLING COMPANY DISPATCH; ATIS; LAS VEGAS RAMP; EXPLAINING TO PAX; ETC! REST OF FLT WAS NORMAL OTHER THAN DEPRESSURIZATION DURING LAST 2000-3000 FT ON FINAL. I FOUND IT USEFUL TO BE NOT FLYING; TO INSURE THE PROPER CALLS AND NOTIFICATION WERE MADE. FO FLYING EXTREMELY SMOOTH; PAX WOULD NOT HAVE KNOWN ANYTHING WAS WRONG EXCEPT FOR THE TURN. SO'S EARLY REACTION; EXECUTION OF CHKLIST; TROUBLESHOOTING AND COMPANY CALLS WERE OUTSTANDING.