Mexican great Saul 'Canelo' Alvarez further added to his legacy by taking the WBO light-heavyweight crown from Sergey Kovalev with a devastating 11th-round knockout in Las Vegas.Middleweight king Canelo, 29, had stepped up two weight divisions to face the 36-year-old Russian.It proved a close fight which failed to ignite before an explosive combination from Canelo ended Kovalev's night.Canelo has now won world titles in four weight divisions.A cagey encounter at the MGM Grand appeared to be heading to a 12th round and one for the judges to decide before a left hook-right hand combination came from nowhere and left Kovalev floundering on the ropes.Judges had Canelo slightly ahead at that point on their scorecards.Canelo, the best-paid fighter in the sport, said winning a title at a fourth weight was an attempt to further enhance his reputation in his boxing-obsessed homeland.He started his career at 139lbs when he boxed as a 15-year-old on debut in 2005 and had won world titles at light-middleweight, middleweight and super-middleweight before this latest victory.Kovalev was a tough opponent in what was his 16th consecutive world title fight, a run which started when he dismantled Briton Nathan Cleverly in Cardiff in 2013.But the victory means Canelo still has just one defeat in 56 fights - against Floyd Mayweather in 2013.Following the fight Canelo said his victory was "to honour the dead, on this, the Day of the Dead in Mexico".He was also asked about who he could face next - a third fight against former middleweight rival Gennady Golovkin has long been mooted."We have to see what happens," the Mexican said."We have to see what's best for us and look for the best fights."Meanwhile, another Mexican, Miguel Berchelt, successfully defended his WBC world super-featherweight title with a fourth-round knockout of American Jason Sosa at the Dignity Health Sports Park, Carson, California.