MIAMI GARDENS, Fla. — The Alabama Crimson Tide moved closer to its third national championship in four seasons with a difficult but authoritative 45-34 win over Oklahoma on Saturday in a College Football Playoff semifinal, a result that surprised just about nobody.

Alabama, ranked No. 1 with a perfect record (now 14-0), did what Alabama does, ultimately subduing a tough opponent to earn a chance to defend the title it won last season against Georgia.

On Saturday at the Orange Bowl here in Hard Rock Stadium, that opponent was the Oklahoma Sooners (12-2), ranked No. 4, with one of the most explosive offenses in college football. But Oklahoma could not overcome its most glaring problem: a defense ranked among the worst of the 130 top-level college teams.