LAS VEGAS — It rained and rained and rained, and then it stopped. Jaime Munguía poured the pressure on Canelo Álvarez early in their scheduled 12-round affair, but in a classic teacher vs. student masterclass, Álvarez weathered the storm, floored Munguía in the fourth round, and successfully defended his undisputed super middleweight title for a fourth straight time before a lively crowd of 17,492 at T-Mobile Arena.