Vladimir Klitschko comfortably retained his WBO heavyweight title, stopping Ray Mercer with a technical knockout in the sixth round of their bout in Atlantic City.

The Ukrainian is now aiming for a fight with Lennox Lewis, who holds the more prestigious WBC and IBF crowns.

"I think I can prove myself with a fight versus Lewis or (Evander) Holyfield or (Mike) Tyson," the 26-year-old Klitschko said after his win at the Trump Taj Mahal Hotel and Casino.

Holding a 15-pound advantage, Klitschko had the 41-year-old Mercer in trouble from the start.

A five-punch combination was followed by a pair of left hooks that dropped Mercer with 30 seconds left in the first round.

Lacklustre opponent

Mercer was hurt by a straight right-hand in the second round and suffered a cut over his right eye in the fifth.

When the end came in the sixth, he did not fight back for more than a minute before referee Randy Newman stepped in and stopped it at the 1:08 mark.

The fight statistics revealed that Mercer, who appeared out of sorts throughout, threw just 10 power punches.

The victory puts Klitschko's record at 39-1 with 36 knockouts.

The 1996 Olympic champion has now stopped 14 of his last 15 opponents.