Complex sentence: In the semi-finals, they met Real Madrid, who won the first leg 2--1 at the Santiago Bernabéu while Atlético won 1--0 at the "Metropolitano".
Split into simpler sentences: In the semi-finals, they met Real Madrid. Real won the first leg 2--1 at the Bernabéu while Atlético won 1--0 at the "Metropolitano".