Real Madrid fans and players celebrated their hard-fought win against Atletico Madrid on Wednesday, earning a quarterfinal berth in the Champions League, but manager Carlo Ancelotti was more relieved than rapturous at what he said was a subpar performance.

Real secured the victory by winning a penalty shootout 4-2, after the tie ended 2-2 on aggregate, as the defending champion's bid for a record-extending 16th European Cup continues.

Ancelotti was disappointed that Real conceded a goal inside the first minute, which leveled the tie after Real had secured a 2-1 first-leg advantage at home last week.

He urged his players to be sharper, as they prepare to face Arsenal for a place in the semis.

"I have tried to explain to my players that the priority was not to make the game more complicated than it already was," Ancelotti told a news conference.

"We made it more difficult by losing unnecessary balls that constantly found us out of position. If they scored 2-0, then the game could have got out of control. We played better as the game progressed, had our chances, but we need to improve in our focus and concentration," he said.

"We always have to look for improvement. The tie was evenly matched, and a mistake could have been costly. We wanted to finish the game before penalties, sure, but here we are, still fighting and in contention, as is customary at this club."