Ukrainian Klitschko, 33, rattled the 27-year-old American in the second round but had to wait until just before the end of the 12th to stage a dramatic finale and knock him out.
Chambers tumbled into the ropes with the referee ending the bout as Klitschko improved his record to 54 wins from 57 fights. Both boxers started off cautiously with Klitschko well aware of "Fast Eddie" Chambers' speed and the American wanting to avoid the Ukrainian's reach. Klitschko used his jab to wear down an opponent who kept moving around the ring.
It did not take long, though, for the 1996 Olympic champion to hurt Chambers with a series of punishing right-hand punches in the second round that rattled his confidence. Klitschko, with brother Vitaly –– WBC heavyweight champion –– in his corner, landed another big right in the third but Chambers bravely battled on while never really staking a strong claim for the titles.
Chambers, with 18 knockouts in his 35 wins, landed few big punches and none powerful enough to hurt Klitschko.
A brief break in the ninth round to change a glove gave Chambers some time to recover but Klitschko looked fitter and stronger throughout, landing the knockout blow five seconds from the bell to inflict Chambers' second defeat in 37 fights.
