Juan Diaz always dreamed of being involved in a Fight of the Year, about lifting roaring spectators to their feet and claiming a place in boxing’s rich lore. And it became reality last year, when he and Juan Manuel Marquez engaged in 2009’s most-riveting contest.

One problem, though: He didn’t lose in his dream.

Diaz is confident he’ll correct that mistake when the two meet again on July 31 in Las Vegas on HBO Pay-Per-View, 17 months after Marquez rallied to score a spectacular ninth-round knockout. In the process, Diaz said, he’ll prove to a growing number of doubters that he’s far from finished.

“I’m excited ÔǪ very excited. I feel blessed to have this opportunity. And I want to take full advantage of it,” Diaz said by phone a few minutes after he finished his afternoon workout on Monday in Houston.

Diaz (35-3, 17 knockouts) believes he dominated the early rounds of the first fight because of his trade-mark pressure and Marquez’s tendency to start slowly. Some observers thought Marquez (50-5-1, 38 KOs) was on his way out, a stunning prospect given Marquez’s No. 2 pound-for-pound ranking.

Then the wily Mexican got rolling and turned the tide. The scoring was dead even — a draw after eight rounds — when Marquez put Diaz down late in the ninth and then flattened him with a monumental right uppercut, prompting the referee to stop the most-exciting fight of 2009.

How did Marquez adjust?

“He’s just a really smart fighter,” Diaz said. “He was catching me falling in, punching me when I was leaning over. He started landing some really good uppercuts and that was it.”

That’s what Diaz said will be different in the rematch — no more leaning.

“I’m definitely expecting another great fight,” he said. “I’m a pressure fighter. That’s what I do. It’s what made me the fighter I am today. I’m just going to be a little smarter this time. I’m not going to square up against him. And I was going straight in with my head down. I’ll still apply pressure but not go in with my head down.”

Diaz was asked whether he believes Marquez is the same fighter after going up in weight to fight Floyd Mayweather Jr. at welterweight — losing badly — and then coming back down to 135 pounds at 36 years old.

Diaz would only say that he hopes so ÔǪ but isn’t counting on it. The Marquez for whom he’s preparing, he said, is the one who gave Manny Pacquiao hell in two fights.

Diaz also was asked whether he’s the same fighter? He didn’t hesitate to discuss that.

The evidence suggesting he has slipped is fairly strong: 2-3 in his last five fights, the brutal knockout against Marquez, a controversial victory and clear loss in two subsequent fights against Paulie Malignaggi at 140 pounds.

And Diaz understands his doubters, understands that pressure fighters who sacrifice their bodies to land punches typically fade more quickly than their more-conservative counterparts.

Diaz acknowledges that aggressive fighters are often shooting stars but counters that he’s only 26, just moving into his physical peak. He insisted that he recovered quickly from the knockout loss, as he does every time he challenges his body.

“Not too much can slow me down right now,” he said. “I might start wearing down at 28, 29, I don’t know. Now, though, I really do feel as good as ever. I might be sore, hurting one day, but I wake up the next day feeling fresh.”

And the Malignaggi losses? He says the matchup was all wrong for him in more ways than one.

First, Diaz felt as if he was a particularly small junior welterweight. The fact he weighed in at 137¼ and 138¾, he said, suggests he was pushing his limits. Malignaggi, a natural 140-pounder, was big and strong compared to Diaz.

Second, he said, the worst style for him is a quick-handed, fleet-footed opponent with the ability to escape his pressure. The first Malignaggi fight, which Diaz won, was a stiff test. Malignaggi had his way in the rematch, winning 8-4 in rounds because Diaz couldn’t touch him.

Third, he said, motivation was a problem. Diaz was coming off the biggest fight — and disappointment — of his career against Marquez. He had trouble getting up for Malignaggi, an opponent he figured he’d beat easily. And he said it was particularly difficult getting up for the rematch because he’d won the first fight.

“I didn’t see the point,” he said.

He sees the point in the rematch with Marquez.

This is a crossroads fight for Diaz. If he wins, he remains a major player with lucrative opportunities. Amir Khan has said he’d like to fight the winner, for example. If Diaz loses, he might be finished as an elite fighter. It’s hard to sell 2-4 in six fights.

Diaz sounds very confident. He’s back at his natural weight. And he knows he can beat Marquez, at least for half a fight.

“I wasn’t the same fighter in the fights against Malignaggi,” he said. “I think it always takes something to spark up the fire you once had. This fight has done that for me. It has lit the fire that was missing.

“This will make me the fighter I once was.”

Michael Rosenthal can be reached at [email protected]