UFC 137 Results: What Did BJ Penn Do Wrong Against Nick Diaz?

As Nick Diaz entered the Octagon for the biggest fight of his mixed martial arts career, you could clearly see the determination in his eyes.

Penn entered after with similar determination but much more emotion.

As action began in what ended up as a loss for the former two-division champ, Penn's emotion carried over as he dominated Round 1 early.

Penn was the aggressor, attacking and pushing his opponent back by throwing a combination of over hands and uppercuts to the body of Diaz.

It was one of the more impressive rounds of Penn's career, as he appeared to be back to the normal "BJ" we all once knew.

But that all changed when the second frame began. Diaz took control.

The tides had turned, as Diaz began to unload his exceptional striking to every part of Penn's body. After a huge right, Penn was rocked but continued to battle through.

While many wouldn't like to admit it, Penn's conditioning was a huge factor—he appeared to be gassed after just the first round.

Diaz, arguably the most well-conditioned fighter in the UFC, continued to swing away at Penn as the final round quickly approached.

When the third round began, Diaz continued to land deadly blows to Penn despite his inability to finish the UFC legend.

Fans across the UFC were more than likely questioning Penn's game plan as he failed to take the fight to the ground.

But, when it came down to it, BJ Penn's conditioning played the final factor in his loss to Nick Diaz at UFC 137. And as others have pointed out based on his televised post-fight interview with Joe Rogan, he may be retiring because he's realized the same thing.