LAS VEGAS — Canelo Alvarez has gone to bed the last few months thinking about how he’s going to knock out Gennady Golovkin in their middleweight title rematch.

But to wake up Sunday as the 160-pound champion, he’ll have to take chances he didn’t in his first fight with Golovkin a year ago. And that could be a real problem against a fearsome puncher who has knocked out 34 fighters in his 39 fights.

“I know it’s going to be a tough fight,” Alvarez said, “but I’m going in there to knock him out.”

Alvarez and Golovkin get another chance to settle what they couldn’t last September when they meet in a rematch of their first fight, which ended in a draw. They do so Saturday night not as the gentleman fighters they painted themselves to be then, but bitter rivals who legitimately seem to dislike each other.

That showed at Friday’s weigh-in, when the fighters had to be separated in their only face-to-face appearance before the fight. Golovkin weighed 159.6 pounds and Alvarez was at 159.4.

A positive test by Alvarez for clenbuterol forced the rematch to be postponed from May. At the same time it produced hard feelings between the fighters over Alvarez’s contention it was caused by eating contaminated meat in his native Mexico.

Whether that translates into a more entertaining fight remains to be seen. But both seem determined not to let it be decided by ringside judges.

“It’s a real fight,” Golovkin said this week. “Like a real war.”

Golovkin (38-0-1, 34 knockouts) is a slight favorite, much as he was in the first fight. Many at ringside thought he won but Alvarez pulled off a draw by taking the late rounds as the 36-year-old Golovkin seemed to fade.

The fight wasn’t the “big drama show” that Golovkin likes to talk about, with neither fighter down and neither really hurt. But it was a tough, competitive matchup that delivered in other ways even without a winner.

“I had a great experience from the first fight,” Golovkin said. “It’s a little bit different this time but I believe it will be a big fight for the fans.”

Alvarez (49-1-2, 34 knockouts) also believes that but sees a different result. It’s one he’s envisioned nightly in bed as he goes over scenarios to help him win.

“Every night in my bed before I go to sleep I visualize what I need to do to get the knockout,” Alvarez said. “I know it’s going to be a tough fight.”

The most popular fighter in his native Mexico, Alvarez has taken a hit from fans both for testing positive and not fighting more aggressively.

He can only talk about the doping that got him suspended for six months by Nevada boxing authorities, but he can do something in the ring to alter the perception that his style is too conservative.

The fight has a pay-per-view price tag of $84.95.