Alcoyano deservedly opened their tally through Javier Lama after 78 minutes, but Benzema wrapped up the win with a cool finish late on.
Here, Sports Mole dissects the 90 minutes of action between the two Spanish rivals.
Was the result fair?
Alcoyano did attack with purpose this evening, but they never really threatened to secure a result. It was one of those games that Madrid would win every single time they played. Jose Mourinho picked a strong team and the difference between the two outfits was there for all to see.
5/10. Alcoyano did not let anyone down with their performance this evening. They had plenty of possession in advanced areas but unfortunately did not have the finishing ability when it really mattered. In truth, bar an absolute miracle, this tie is over. But they will take heart from their performance.
4/10. It was hardly vintage from Madrid, but in truth it didn't need to be. They played the whole match in first gear and never had to raise the tempo. It is always difficult to judge the quality of a performance when there is such a big gap between the two teams.
Sports Mole's man of the match
Karim Benzema: The Frenchman has not hit top form in the league for Madrid this season, but he scored two goals this evening in a strong all-round performance.
Madrid's passing was ever so wasteful for large periods of the match. Granted they scored four goals, but against better opposition they would have struggled.
Fernando Teixeira Vitienes had a fairly straightforward 90 minutes of action this evening. The Spaniard went unnoticed for large periods which is always a good sign for a referee.
Alcoyano: Alcoyano return to domestic action against Ontinyent on Sunday when they will attempt to make it seven league victories in a row.
Madrid: Mourinho's side will attempt to continue their strong form in La Liga when they welcome Real Zaragoza on Saturday.