Real Madrid, the 10-time winner, played out a goalless draw at Manchester City, a team making its debut in the last four of Europe's top club competition.
The result suits Real, which was deprived of its star player Cristiano Ronaldo, who failed to recover from the thigh problem which had troubled him over the past week.
The second leg in Madrid which takes place next Wednesday should allow Madrid to progress to the final with Ronaldo expected to return for a club which remains the most successful in the history of the competition.
Real, which also lost Karim Benzema to injury at halftime, created the better chances and only a series of fine saves by Joe Hart, the Manchester City goalkeeper, denied the visitor.
In Champions League games without Ronaldo, Real has a win ratio of just 43% -- down from 71% in the contests where he's been involved.
"We knew they were going to play a slow game and that is why we pressed as a team," Manuel Pellegrini, the Manchester City manager, told BT Sport.
"When we had the ball, we could not make the difference. We could not score.
"This season we have played very well away. Now we go to the Bernabeu with the same attitude as playing at home.
"Real Madrid must attack a little bit more. You cannot take too much from the first leg, we can see from the second leg who will go through."
For Manchester City, this was a step into the unknown. Never before had the club managed to progress to the last four of Europe's most prestigious club competition and yet in its path, stood the one of the game's most illustrious opponents.
Real Madrid, in the semifinals for the sixth year in succession and 27th occasion overall, has been in imperious form in recent weeks and City's cause was done little favor by the loss of David Silva to a hamstring injury.
Last weekend, Real came from two goals down to defeat Rayo Vallecano and seal a ninth consecutive league victory.
But the goals dried up on this occasion as Hart, the City goalkeeper, kept the visitor at bay.
Real, which hit the bar through Jese in the second half, went close again when Casemiro's header was wonderfully saved by Hart.
The City goalkeeper then produced an outstanding block to thwart Pepe from close range with the Real defender appearing certain to score.
Real, which was rarely tested in a defensive capacity, will now hope to qualify for next month's final in Milan.
It will face either Bayern Munich or city rival Atletico Madrid with the duo set to meet on Wednesday.