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* Double strikes for Ramos and Ronaldo secure 4-0 win
* Dazed holders Bayern stunned by attacking onslaught
* Real to face Chelsea or Atletico Madrid in the final
By Brian Homewood
MUNICH, April 19 (Reuters) - Real Madrid tore Bayern Munich apart with three goals in 18 astonishing first-half minutes to reach the Champions League final with a 4-0 win on a dreadful night for the holders at a stunned Allianz Arena on Tuesday.
Two headers from Sergio Ramos, a breathtaking breakaway goal by Cristiano Ronaldo and a late free kick by the Portuguese forward in a one-sided semi-final, second leg handed Bayern their heaviest home defeat in European competition.
Bayern, beaten 5-0 on aggregate, were impotent in attack and ragged at the back and their performance left a stain on the reputation of their former Barcelona coach Pep Guardiola.
Goalkeeper Manuel Neuer's South American-style forays out of his penalty area had the home fans living on the edge while Bayern's shocked players reacted petulantly to a number of tackles as they lost their composure.
The third goal summed up Real's counter-attacking performance as they broke from their own penalty area to score in a matter of seconds.
Gareth Bale played the ball to Angel Di Maria, who released Karim Benzema on the right, with the Frenchman playing the ball inside to Bale and he quickly sent a pass to his left where Ronaldo slipped the ball past Neuer.
Real, who will face Chelsea or Atletico Madrid in the May 24 final, did to Bayern exactly what the Bavarians had done to Barca last year when a 7-0 aggregate semi-final win had pundits predicting an era of dominance for the Munich side in Europe.
"It was a perfect game, especially the first half when we defended very well, using a very efficient counter-attack, with passes on the ground, using the speed of the forwards," Real Madrid coach Carlo Ancelotti told reporters.
"We prepared the set pieces very well, the first two goals, and the game was easier after that."
The only disappointment for the Italian was a yellow card for midfielder Xabi Alonso who will miss the final as a result.
Bayern, previously unbeaten in nine home meetings against Real, duly wrapped up the Bundesliga title this season with seven games to spare but have suffered a dramatic loss of momentum since then.
Spaniard Guardiola's tactics have been described as too clever for his own good, with German critics saying Bayern's possession-based game has become predictable and toothless but he said he would stick by his tried and trusted methods.
"I know it's a tough night for us for me and for the players," he told reporters. "The reason we did so badly in the first half is that we did not have possession. We didn't play with the ball."
Nine-times champions Real, meanwhile, are back in the final after a 12-year absence which has included four semi-final defeats, including the last three seasons, one quarter-final loss and six round of 16 eliminations.
Bayern, trailing 1-0 from the first leg, laid siege to Real's goal early on while the crowd attempted to intimidate the Spaniards by whistling incessantly when they had possession.
But, although they huffed and puffed, the hosts rarely threatened and there was always a risk they would concede a killer away goal.
That arrived in the 16th minute when Ramos rose unmarked at the far post to score with a powerful downward header.
Amid general disbelief, Real struck again four minutes later when Angel di Maria's free kick was flicked on and Ramos headed into the corner.
The setback saw Bayern lose their composure, leaving them wide open to Real's ruthless counter-attacks, including Ronaldo's effort just past the half hour.
There was an incredible moment shortly afterwards when Neuer came racing out of his goal and sent his clearance to Ronaldo who tried to score from 40 metres but saw his shot bounce over.
Guardiola tried to limit the damage after halftime by replacing his only striker Mario Mandzukic with defensive midfielder Javi Martinez.
Arjen Robben then produced the home side's best effort with a shot which curled narrowly wide just before the hour.
However, a dazed Bayern side looked almost relieved to be only 3-0 down until Ronaldo sent a free kick under the wall in the last minute to complete an astonishing evening for Madrid. (Reporting by Brian Homewood; editing by Alan Baldwin and Ken Ferris)