Devon Alexander said he needs “a defining fight” against Amir Khan in their welterweight clash at the MGM Grand in Las Vegas on Dec. 13.

“I’m still improving. I’m only 27 and I have a lot to prove. I need to look exceptional with an exceptional fighter and with a fighter of a high caliber like an Amir Khan,” said Alexander, a southpaw who is 26-2 with 14 knockouts.

“I need to go in there and dominate him and to look good, doing it with a spectacular performance. Then people are going to say, ‘Okay, I can respect this guy,’ and ‘I know what this guy is capable of doing.’ I need a defining fight, as they say.”

Promoted by Golden Boy Promotions, Alexander-Khan will be the main event of a Showtime tripleheader that will include Keith Thurman and Leonard Bundu in a 147-pound clash of unbeatens and undefeated junior middleweights Jermell Charlo and WBO titleholder Demetrius Andrade.

Also on the card will be three-division titlist Abner Mares in a featherweight bout and former welterweight beltholder Victor Ortiz. Mares and Ortiz will fight opponents to be determined.

Alexander is coming off a unanimous decision victory over Jesus Soto Karass in June after having been dethroned as IBF 147-pound beltholder in a unanimous decision loss to Shawn Porter last December.

Alexander had previously faced seven current or past titleholders in his last nine fights, a run that includes decision victories over two of Argentina’s most devastating punchers – Marcos Maidana and Lucas Matthysse.

“I showed people that I can mix it up. I can stand there and bang or I can box if I need to and use my speed if I need to and just utilize whatever he is trying to do against him. I can stand in the pocket, catch and shoot. I can take some because [Soto Karass] did catch me a couple of times with some good shots. Overall, I had no problem with that,” said Alexander, whose only other loss was to two-division titlist Timothy Bradley as junior welterweights in January 2011.

“But I like that some people don’t give me credit because if people don’t think that I looked that good, then that tells me that they have higher expectations of me, which is good. I don’t mind that. People know what I’m capable of doing, so, I’m okay with that. I thought that I did a C or a C-minus but I’m my own worst critic myself. So I am always going to think that I can do better. It was a good win, nonetheless, but I just took from that fight that I can do whatever it takes to win a fight.”

“What I take from the Bradley and Porter fights is that I wasn’t mentally prepared for their rough tactics. I was just focusing on what my game plan was. Mentally, you have to know that this guy is rough and this guy is going to do this or that and be prepared for that. For both of those fights, mentally, I didn’t get into that mode or into that groove,” said Alexander.

“People may say that if you pressure Devon then he’s going to crack. But no, I’ve fought plenty of pressure fighters and people who have tried to muscle me. It’s not that. The time that I fought and lost, it was something that I didn’t do. I know that I could have beaten both of them but it’s just that, mentally, I wasn’t there. I’m way better than those performances and I’ve just got to show people that. As I’m getting older, I’m learning more about those mistakes that shouldn’t happen.”

Entering his match with Maidana in February 2012, there were some observers who felt Alexander had lost his previous three bouts against Andriy Kotelnik, Bradley and Matthysse. Alexander, meanwhile, dominated Maidana, winning by scores of 99-91 and 100-90 (twice).

“Soto Karass was a good fighter. Everybody knows that he’s tough and he’s going to test you and he’s going to bring it out of you. I thought that I handled it pretty good. I showed people some things that they’ve not seen from me lately.

“I had a defining fight against [Juan] Urango that sort of introduced me on to the scene. That was the fight that let the world know who I was and at the time, it showed that I was one of the elite in that division. I think that’s why people criticize me so much. They know that I’m better than the performances in my two losses. So I need something like that again to refresh people’s minds. I need to remind them why they thought that I was one of the elite or that I still can be one of the elite,” said Alexander, whose eighth-round technical knockout in March 2010 added Urango’s IBF 140-pound belt to Alexander’s WBC title.

In his last fight in May, Khan (29-3, 19 KOs) scored a one-sided unanimous decision over former welterweight titleholder Luis Collazo, a southpaw whom he floored three times on the undercard of the first Floyd Mayweather-Maidana bout.

Khan, 27, had been out of the ring for almost a year prior to the Collazo fight, last being in action for a unanimous decision over two-time lightweight titleholder Julio Diaz in April 2013. Khan struggled over the course of his previous six fights, going 4-2 with two knockouts.

Alexander was supposed to face Khan rather than Porter but Khan declined, believing Mayweather would elect to fight him in May. Instead, however, Mayweather chose Maidana.

“Khan was forced to take this fight. He’s under pressure because he wants to fight Floyd Mayweather, so he wants to prove that he can beat a top fighter. There are talks about him fighting Mayweather and this and that and I’m fine with that. He took this fight because he wants to prove himself worth of having a Mayweather fight,” said Alexander.

“I’m not stupid. I see the picture. So I’m honored to know that I’m an elite fighter and that I’m capable of knocking Amir Khan out. But that’s not what I come to do necessarily. I come in to beat the guy in front of me, whatever they bring to the table. People want to see what I still got and if I can still perform at the elite level. They want to see how I react to it. I know that this is a business and I’ve got to be on my game and beat this guy.”