The Ukrainian knocked Austin down 87 seconds into the round with two left hooks. The American climbed to his feet, but the referee stopped the fight, according to AP.
Klitschko improved his record to 48-3 with 43 knockouts in the mandatory defense, while Austin fell to 24-4 with four draws and 16 knockouts.
Both fighters were listed at 6-foot-6 and 246 pounds, with Austin`s camp hoping another big heavyweight would trouble Klitschko. But the champion measured Austin with his left hand for the first round and then caught him on the ropes with two blows seconds apart to end the bout.
The crowd of 15,000 roared for Klitschko when he marched in, then jeered a fight with just two or three punches landed.