Real Madrid forward Karim Benzema celebrates after scoring a goal against Atletico Madrid at the Santiago Bernabeu stadium in Madrid on Saturday. Photo: AFP

Zinedine Zidane's double substitution at halftime transformed the Madrid derby on Saturday as Real Madrid edged past Atletico 1-0 to remain top of La Liga. 

Karim Benzema scored the winner at the Santiago Bernabeu after Zidane's decisive intervention turned a contest that Atletico had dominated into another comfortable Real Madrid victory. 

Vinicius Junior, one of the substitutes, was also key to the goal. 

"I wasn't happy with what I saw but it's not down to the players, it's my responsibility," Zidane said. "We had to make a change."

While Diego Simeone's side were strong in the first half, they were yet again blunt in front of goal and then failed to respond when their opponents found a different gear.

This is Atletico's fifth game without a win and on this form, they might begin to worry about missing out on Champions League qualification. 

It is a far cry from preseason when they thrashed Real 7-3 and many were tipping them as serious challengers. 

Zidane was under pressure then but his team are on a relentless run, now 21 games unbeaten, the latest due in large part to his changes. 

The decision to ditch a failing system and revert to 4-3-3, with Vinicius Junior and Lucas Vazquez coming on for Isco and Toni Kroos, was both brave and effective. 

Real's form is impressive and they have Eden Hazard, out since November, on the brink of a return, perhaps on Thursday in the Copa del Rey quarter­finals against Real Sociedad. 

Gareth Bale's absence was not related to fitness. The Welshman was left out of the squad despite training for most of the week after an ankle injury. 

"He was available," said Zidane. "I had to choose and I chose someone else. But it's not a big issue and I'm counting on him until the end."

Simeone's side were significantly ­better in the first half and should have taken one of a handful of decent chances as Vitolo hit Thibaut Courtois, Saul Niguez flashed wide and Angel Correa poked past the post after going through one-on-one, even if he probably would have been called offside.

Casemiro was fortunate not to concede a penalty when he clumsily fell into Morata. 

Real Madrid's cluster of central midfielders looked unsure of their 4-3-2-1 shape. Fede Valverde looked particularly uncomfortable as he spent much of the first half as a right winger. Luka Modric was virtually anonymous in his more advanced role. 

Zidane's double change was a recognition of Atletico's superiority as he reverted to the more familiar 4-3-3 with Modric deeper in midfield. 

The balance shifted immediately. Real dominated the start of the second half.

In the 56th minute, Vinicius cut in from the left and slipped in the overlapping Ferland Mendy, whose cross to the back post gave Benzema a simple finish. 

Atletico had been weakened shortly before when Alvaro Morata, perhaps the best player on the pitch in the first 45 minutes, went off with an injury. He was replaced by Thomas Lemar, whom Simeone expected to be sold in the January transfer window. 

Real retreated a little, perhaps waiting for an Atletico push that never came.