The big Ukrainian caught Donald with a right in the round, sending the American to the canvas for the first time in his career.

Klitschko, 32-1 with 31 knockouts, then went after Donald with a vengeance, hitting him with a flurry of punches.

The American went down four more times, twice because the Ukrainian flung him to the canvas.

Donald, reeling away from some more punches, then fell over for a fifth time, this time because his wobbly legs collapsed, and the fight was over.

"Nobody had knocked him out because he's fast and an uncomfortable opponent, but I did it," said Klitschko.

Klitschko found out just hours before the fight that his wife gave birth to a baby girl.

Now, after a successful return to the ring, he is expected to face Lewis for the WBC title in the spring.

"I look forward to fighting Lewis in three or four months. I will do my best so that it turns out like this fight," said Klitschko, 31.

The mobile Donald began to slow down with every round. He occasionally attacked in small bursts, but he also often stood flatfooted in the latest rounds - as the anticipation rose that the knockout might be close.

Donald, 35, has never had a title fight and may now never get the chance. He has beaten Tim Witherspoon, but lost his only other big fight to Kirk Johnson.