Vitali Klitschko defended his WBC heavyweight crown, but the effects of aging clearly slowed the 40-year-old champ.

Klitschko defeated the brash Dereck Chisora by unanimous decision, but it was far from a dominant performance. In the early rounds, Klitschko landed a flurry of big right hands, and it looked like Chisora wouldn't be able to touch him.

But in the middle of the fight, Chisora was able to hurt Klitschko with repeated blows to the body. He negated Klitschko's reach advantage, bobbing and weaving his way into the interior of the big Ukrainian's defense.

Klitschko was able to hold on, but he didn't look anything like the machine we've become used to seeing. He didn't look dominant. He didn't look invincible. He looked...forty.

After a 16-year professional career, Klitschko's age is finally showing. He landed some hard punches, but they lacked that usual Klitschko pop. He also struggled with his endurance after the eighth round, breathing heavily with his mouth open.

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Klitschko eventually registered the 44th win of his career, but it was only the fourth that didn't end in a knockout. Given the pre-fight antics Chisora was pulling, this was more than a little surprising.

I was expecting Klitschko to come out with murder on his mind. I thought he was going to batter Chisora into a bloody pulp, asserting his dominance over the rest of the heavyweight division. Instead, he stumbled his way to an unimpressive victory.

Klitschko acknowledged after the fight that he wasn't happy with himself.

“I’m not proud of my performance tonight because I feel I let my fans down,” Klitschko said.

Although that comment usually isn't uttered by the winning fighter, it's a testament to the standard Klitschko has set for himself. Unfortunately, as he enters AARP territory, Klitschko's age will no longer allow him to spank top-notch opponents like they're spoiled children.

Klitschko still has a stranglehold on the WBC heavyweight title, but he's not the force he once was. Yes, he still won the fight. And yes, he'll be the favorite in his future fights. However, his days as the god of boxing are nearing a close.

Klitschko has had a dream career, but unfortunately, the reality of age is finally settling in.