Real Madrid coach Manuel Pellegrini admitted concern over defensive lapses after their 3-2 win over Atletico.
Real returned to the top of the Primera Division table after beating Atletico to record their 15th league victory out of 15 at home this season and extend their current winning streak to 11 matches.
It also continued Real's remarkable recent record against their bitter rivals, which has left Atletico without a derby win since 1999, but they had to do it the hard way on Sunday night after falling behind to Jose Antonio Reyes' 10th-minute opener.
Real had a couple of chances to draw level before the break, but it was not until the second half that they finally got into gear, scoring three times in 13 minutes through Xabi Alonso, Alvaro Arbeloa and Gonzalo Higuain to go 3-1 up.
However, Real were left with a nervy final 22 minutes after Atletico pulled a goal back through Diego Forlan's penalty.
The title-chasers ultimately held on to their lead without too many concerns, but Pellegrini felt the final scoreline was closer than it should have been.
"It was important to play well in the second half. We scored three goals and we had chances to get more. We knew what we had to do and I think the penalty was a gift that gave Atletico confidence," he said.
"Although we scored three goals, it's worrying that our opponent, almost without creating any chances, scored two goals.
"We were too static during the first half, but we had chances to equalise and we didn't take them. (However), we were superior to Atletico Madrid throughout the match.
"The football we played was enough to beat Atletico, which is the most important thing."