Real Madrid's Mesut Ozil from Germany, unseen, celebrates his goal with Cristiano Ronaldo from Portugal, centre, and team mates during a Spanish La Liga soccer match against Valladolid (Photo: AP)
After finishing second in Group D behind Borussia Dortmund, Real will play one of group winners Manchester United, Juventus, Paris St Germain, Schalke 04 or last year's runners-up Bayern Munich, who knocked them out on penalties in the semi-finals.
It is not difficult to imagine Bayern's Mario Gomez, PSG's Zlatan Ibrahimovic or United's Robin van Persie capitalising on the defensive frailty Real showed at Valladolid as they twice allowed Manucho to score from corners.
The powerful Angola forward's first came after the Real defenders failed to clear a loose ball and he was quickest to react, smashing shot past Iker Casillas from close range.
He then grabbed a second when he nipped in front of his marker, Spain centre back Sergio Ramos, and crashed a header into the top corner.
Both set pieces were taken by Valladolid's German midfielder Patrick Ebert and all five of Real's potential Champions League opponents have players of similar ability in delivering the ball into the danger areas.
"It cannot be denied that we need to improve when defending the set piece," Ramos told reporters. "We made mistakes, above all in the first half," added the 26-year-old, one of Real's club captains.
Assistant coach Aitor Karanka, standing in for Mourinho at Saturday's post-match news conference, acknowledged Real's defensive weakness but praised the players for twice coming from behind to win the game.
It was not the first time this season they have conceded from set pieces and their 1-0 La Liga defeat at Sevilla in September came after an unmarked Piotr Trochowski netted from a corner in the second minute.
"We made mistakes at the set piece but you have to remember that they are isolated incidents and can be corrected," Karanka said.
"We should focus on the team's capacity to come from behind and twice they were able to overcome those two errors.
"We fought back to win a tough game and secured an important victory."
The draw for the last 16 of the Champions League, when Real will continue their bid for the 10th European title, will be made on Dec. 20.
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