Zinedine Zidane blamed himself for the slow start to Real Madrid's 1-0 defeat of city rivals Atletico at the Bernabeu.
Atletico enjoyed the best of the first-half chances but the game remained goalless at half-time, inspiring Zidane to replace Toni Kroos and Isco with Lucas Vazquez and Vinicius Junior respectively.
The rotation seemed to have its intended effect as it was only a minute later that Karim Benzema converted a Ferland Mendy cross into the match-winning goal for the LaLiga leaders.
"I wasn't happy with what I saw on the pitch in the first half," Zidane said at the post-match press conference.
"It wasn't the players' fault. It was mine. So I changed Isco and Kroos, but I could have changed two others players.
"It was just that we needed to make a change to play in a different manner, we were much better in all aspects afterwards.
"There was more intensity, but I repeat, the responsibility for the first half is mine."
Vinicius, who fed the ball to Mendy before Benzema's goal, earned praise for his performance after immediately gelling with the French left-back.
"They did well," said Zidane, whose side moved six points clear of second-placed Barcelona, who have a game in hand.
"They both worked hard. The goal says it all. I think there was also a good connection between Lucas Vazquez and Dani Carvajal on the other side."
The 47-year-old also spoke of the added significance of enjoying a victory against the team on their doorstep, saying: "A derby is always special and complicated.
"Against a team that defends really well, this was a good win. I think it was a deserved victory and three points."
Atletico manager Diego Simeone rued his side's inability to capitalise on their first-half dominance, saying to the club website: "We played well.
"We were very good in the first half and had chances to score, but were unable to take advantage of our superiority in the opening 45 minutes.
"Real Madrid started the second half well and scored following a nice play. We pushed to equalise until the end. We have to keep working hard and think about the upcoming match."