HANNOVER, Germany (AP) _ Dariusz Michalczewski of Germany defended his WBO light heavyweight title Saturday night by flooring Nicky Piper three times before the Welsh challenger's corner stopped the fight after seven rounds.

Michalczewski, 35-0 with 28 knockouts, sent Piper flying across the canvas with a left hook just 24 seconds into his lopsided 10th title defense, then dropped him to his knees later in the first round with a hard left.

The Polish-born Michalczewski also crumbled Piper with a hard right midway through the seventh round. The Welshman, known for his ability to take a punch, rode out the round but was pounded ferociously.

The corner of Piper, 26-5-2, threw in the towel after the round.

``I tried to hit him early, but he caught me. After that I didn't have the strength,'' said Piper, 31, who said afterward he would give up boxing.

``He was back and he was a threat,'' Michalczewski said. ``But I thought, I won't back up, I'm going in with my canons.''

Michalczewski next wants a reunification fight against WBC champion Roy Jones _ considered by many the best pound for pound fighter in the world.

The improving Michalczewski, 29, has learned to throw his strong right along with the left hook he relied on too heavily while piling up early knockouts against overmatched opponents earlier in his career.

Piper led former WBO champion Leeonzer Barber in a 1994 title bout but lost when the fight was stopped in the ninth round because of a cut. He also lost to Nigel Benn for the WBC super-middleweight belt.

Piper, after the early knockdowns, rode out the next four rounds, then appeared to make a comeback in the fifth, which he ended with a flurry of punches.

Piper, who entered with 21 knockouts in 34 fights, then fought stronger over the next two rounds before a right to the chin floored him again.