Benzema, who also scored in the 2-1 win over Sevilla at the weekend, struck in the 40th minute with his 12th league goal of the campaign – three more than anyone else in LaLiga. 

Athletic created enough chances to claim at least a point at the Santiago Bernabeu, yet it was unable to find a way past Thibaut Courtois. 

A fifth league win in a row lifted Carlo Ancelotti's side well clear of second-placed Atletico Madrid, although Diego Simeone's men have a game in hand.

Unai Simon twice denied Benzema from close range inside the opening 15 minutes as Madrid started brightly.

Athletic grew into the game, though, and twice went close before the half-hour mark, Inaki Williams seeing an effort deflected narrowly wide and an unmarked Raul Garcia heading straight at Courtois.

Madrid went ahead five minutes before the interval, Benzema sliding into an empty net from Luka Modric's mishit shot after Simon had thwarted Marco Asensio.

Toni Kroos whipped wide after a fine team move shortly after the restart, before Lucas Vazquez denied Dani Garcia a near-certain goal at the other end with a superb block. 

Unai Nunez inexplicably headed wide from an inswinging free-kick with 20 minutes remaining, while Courtois raced off his line to deny Oihan Sancet as Athletic ultimately fell short of finding the leveller.