Overeem overwhelms Brock in Round 1

It was no secret what Brock Lesnar and Alistair Overeem wanted to do in their heavyweight title elimination showdown.

Lesnar needed to get Overeem off his feet; the former Strikeforce titleholder was determined to deliver strikes.

Striking proved to be the key in this fight and Overeem made it work in his favor. He hit Lesnar with hard knees to the body, each doing more damage than the one before.

A little more than two minutes into the fight, Overeem connected with a knee that sent Lesnar to the canvas. Overeem jumped on the fallen former UFC heavyweight champion with punches and the fight was stopped at 2:26 of the opening round.

Overeem (36-11, 1 no contest) raised his hand in victory, then promised to punish current UFC titleholder Junior dos Santos.

But it's what happened next that will be talked about more than Overeem's success in his UFC debut.

Lesnar officially announced that his fighting days inside the Octagon are over.

"I've had a difficult couple of years with my disease [diverticulitis]." Lesnar said. "I'm going to officially say that tonight is the last time you are going to see me in the Octagon."

Lesnar's career as a mixed martial artist was brief. He fought just eight times, compiling a 5-3 record (4-3 in UFC), but he accomplished a lot in that short period of time.

He would capture the UFC heavyweight title in just his third UFC fight, defeating Randy Couture at UFC 91. Lesnar would go on to defend his belt twice before losing it to Cain Velasquez at UFC 121.

Though Lesnar has proven to be a huge drawing card for UFC, his departure is softened by the arrival of Overeem and a slew of other Strikeforce heavyweights.

Diaz punishes Cerrone with punches

Donald Cerrone entered the cage for the fifth time this year, but he was facing his stiffest test in Nate Diaz.

The result was very different than the previous outings.

Diaz pressured Cerrone from the opening horn with nonstop punching. The judges were impressed with Diaz's punching output and awarded him the decision. All three judges favored Diaz -- 30-27, 30-27 and 29-28. ESPN.com had Diaz winning 30-27.

ESPN.com had Diaz winning this lightweight battle 30-27.

From the opening round, Diaz landed right-left punch combinations that repeatedly found Cerrone's chin. After absorbing so many punches, Cerrone's mouth was filled with blood.

But Cerrone fought hard in the second round, sending Diaz to the canvas several times with sweeping kicks. Each time Diaz hit the floor, he got up immediately.

The kicks served to make Diaz increase his attack in the third round.

Diaz (15-7) came out for the final round so confident he was ahead on points that he started taunting Cerrone. He began talking to Cerrone and dropping his hands -- inviting his opponent to throw strikes.

The two exchanged harsh words before the fight, but their attitudes softened after the final horn.

"I trained hard," Diaz said. "I've got really good training partners Gilbert Melendez, Jake Shields, Nick Diaz.

"I'm glad I got the win. I apologize for all that stuff I said to Cerrone. He came to fight. It was just TV stuff."

Cerrone did not look sharp physically. It might have been due to fighting so often this year, but Diaz kept the pressure on him and that had to take some steam out of him.

Fighting for the fifth time this year, Cerrone had won his previous four bouts. The loss to Diaz puts his professional mark at 17-4 with 1 no contest.

Hendricks makes quick work of highly rated Fitch

Jon Fitch is considered one of the best mixed martial artists in the world, and not just at welterweight.

Fitch is regularly included on many pound-for-pound lists. But that was before he met hard-punching Johny Hendricks.

Moments into their 170-pound battle, Hendricks found Fitch's chin with a powerful left hook. The fight officially ended in 12 seconds.

Fitch went to the canvas as soon as the punch landed and the referee jumped in to protect the former No. 2-rated welterweight.

"I have a left hand. Everybody's been counting me out," said Hendricks, who improved to 12-1. "I knew if I hit him with it, I could lay him out."

Fitch was hoping a victory would get him back line for a title shot. He falls to 23-4-1 with 1 no contest.

Gustafsson's jab finds Matyushenko's chin

It didn't take long for Alexander Gustafsson to win his fifth fight inside the Octagon, but he got a little help from Vladimir Matyushenko.

Gustafsson stopped Matyushenko at 2:13 of the first round. Matyushenko walked into a stiff left jab that sent him to the canvas.

Once his opponent was hurt, Gustafsson pounced on him. Matyushenko was unable to defend himself and the fight was waved off.

"I was prepared for three hard rounds. He's a tough guy," Gustafsson said. "But I got the knockout. It was my day today. It was the biggest win of my life."

Gustafsson, who has won four fights in a row, improves to 13-1. His lone loss came against Phil Davis at UFC 112 in April 2010.

Matyushenko, who had hinted at possible retirement before this fight, slips to 26-6.

Hettes defeats Phan with ease

No one could have imagined Jim Hettes having such an easy time against Nam Phan in their featherweight bout.

It wasn't close.

Hettes dominated Phan from the opening horn en route to a lopsided unanimous decision.

The judges scored the fight 30-25, 30-25 and 30-26. ESPN.com scored it 30-25.

With the win, Hettes improves to 10-0. Phan, who lost for the third time in four fights, falls to 17-10.

Pearson beats Assuncao in featherweight debut

Ross Pearson stepped into the Octagon for the first time as a featherweight and came away with a unanimous decision over Junior Assuncao.

Moving from lightweight to 145 pounds took some getting used to for Pearson. Assuncao was able to take him down early in the opening round.

Pearson also struggled to find his striking range. But in the second round Pearson was able to close the gap and started landing hard strikes.

Once Pearson (13-5) found his rhythm, he held on to it.

Two judges scored the fight 29-28; the third had Pearson winning all three rounds for a 30-27 result.

Assuncao, who came into the bout on a seven-fight win streak, falls to 13-5.

Castillo earns split over Njokuani

Lightweight Danny Castillo agreed to fight Anthony Njokuani a few weeks after a bout in November.

But Castillo showed little signs of fatigue and held on to earn a split decision.

Two judges saw the fight for Castillo 29-28. The third gave Njokuani the edge 29-28.

Castillo, who was able to use his superior wrestling skills in the first and second rounds to control Njokuani, expressed disappointment in the scoring. He also expressed dismay at fans' booing after the decision.

"I thought it [the fight] was close but not controversial," said Castillo, who improved to 13-4. "He's dangerous."

Castillo earned a first-round TKO over Shamar Bailey at UFC 139 on Nov. 19. He has now won two fights in a row.

Njokuani (14-6 with 1 no contest) has won just two of his six most recent fights.

Hard-kicking Kim settles for decision win

Dong Hyun Kim rebounded from a first-round knockout to Carlos Condit in July with an impressive win over fellow welterweight Sean Pierson.

Kim won the standup battle with solid punches and kicks. He nearly finished Pierson in the second round with a front kick to the jaw with seconds remaining before the horn.

The kick stunned Pierson, but he held on long enough to survive. But the damage proved too much and Pierson showed little in the final round.

Kim (15-1-1 with 1 no contest) won each round on all the judges' scorecards en route to a 30-27 advantage. Pierson falls to 11-6.

Volkmann survives upset-minded Escudero

Jacob Volkmann proved too strong for Efrain Escudero during their lightweight bout.

Volkmann was able to get Escudero to the ground during first two rounds and control the action en route to a unanimous decision victory.

All three judges scored the bout in favor of Volkmann, 29-28.

While spending the majority of this bout on his back, Escudero (18-4) nearly pulled out the win in the third round. He caught Volkmann (14-2) in a North-South choke, but was unable to complete the submission.

After the win, Volkmann made another attempt at baiting President Barack Obama. But the joke did not go over well with an overwhelming majority of fans in attendance.

In January, Volkmann made headlines after challenging the President to a fight after his split decision win over Antonio McKee at UFC 125. Volkmann later apologized for his comments after a visit from federal agents.

Nunes kicks his way past Gamburyan

After dropping his two most recent fights, former featherweight top contender Manny Gamburyan was in dire need of a win against Diego Nunes.

But Nunes connected repeatedly with kicks to Gamburyan's left thigh. The impact of the kicks caused a bruise to form on Gamburyan's left leg.

The offensive strategy impressed all three judges, each of whom scored the fight for Nunes 29-28.

Nunes dominated the first and third rounds with his kicking. But Gamburyan gave him a scare in the second by landing a hard right hand.

The punch wobbled Nunes briefly, but he held on to survive the round.

Nunes improves to 17-2. After dropping his third fight in a row, Gamburyan slips to 11-7.

Franklin McNeil covers MMA and boxing for ESPN.com. He also appears regularly on "MMA Live." Follow him on Twitter at http://twitter.com/Franklin_McNeil.