Through 44 fights, Floyd Mayweather has remained untouchable. On Saturday, the undefeated boxer will face one of the toughest challenges of his career.

Saul “Canelo” Alvarez has also never lost since he started boxing professionally. At 42-0-1, he hasn’t fought an opponent anywhere near as good as Mayweather. However, he could pose a serious threat to the 36-year-old’s perfect record.

The online betting Web site Bovada has Alvarez as a plus-220 underdog, giving him a realistic chance to pull off the upset. He attempts to make history at the MGM Grand in Las Vegas on Sept. 14.

Will Alvarez be able to do what no boxer has been able to accomplish? Below are three things to watch for in Saturday’s big fight?

Can Alvarez be patient against a defensive specialist?

Many boxers have tried, but none have been able to hit Mayweather with much consistency. Alvarez, though, is confident that he’ll be the one to figure out the best pound-for-pound fighter in the world.

“My team and I are working physically and mentally hard for this fight,” Alvarez told a Mexico radio station last month. “I’m sparring with fighters with Mayweather’s style. It’ll be hard but I will pierce and break his defense.”

CompuBox, which tracks statistics for all major boxing events, reports Mayweather’s opponents have landed just 16 percent of their punches. Alvarez can’t be too eager, or his efforts will go wasted.

If anyone can have success against Mayweather, it might be Alvarez. He’s the only boxer who connects on a higher percentage of his jabs than Mayweather.

Can Mayweather land power punches?

Mayweather is best-known for his ability to avoid getting hit. Against a strong fighter like Alvarez, though, he may need to land some serious blows in order to secure his 45th career victory.

If his fight against Robert Guerrero is any indication, Mayweather might not have a whole lot of trouble with his power punches. According to CompuBox, Mayweather landed 60 percent of his power punches in his last bout.

Alvarez is the most accurate fighter that Mayweather has faced in quite some time. It will be important for him to establish a strong offense to go along with his impeccable defense.

Who has the endurance to win late rounds?

The odds are that the Sept.14 fight will go the distance. In 87 combined fights, neither boxer has ever been knocked out, and the favorite, Mayweather, has been taken to 12 rounds in five of his last six victories.

Mayweather is much more used to lengthy fights. Alvarez has gone more than six rounds in just half of his previous 10 bouts. According to Ricky Hatton, who was knocked out by Mayweather in 2007, Alvarez will tire as the fight moves along.

“Floyd will make Alvarez miss,” Hatton told BBC Sport.” Any boxer will tell you that there’s nothing that tires you out more than hitting fresh air continually.”

Alvarez has trained himself so that he can be effective in the later rounds. However, Mayweather should have the edge as the final bell draws closer.