Arsenal must overcome a 2-0 first-leg deficit if they are to advance to the semi-finals of the Women's Champions League after losing to Real Madrid on a pitch Gunners legend Ian Wright labelled a "disgrace".
A mistake by England captain Leah Williamson allowed Colombia forward Linda Caicedo to fire the hosts ahead midway through the first half in Spain's capital.
The 20-year-old produced a composed finish in what was Real's only attempt of the first half on target after Williamson failed to cut out a pass to Caicedo.
Arsenal found it heavy going in wet conditions at Estadio Alfredo di Stefano on what was a dreadful pitch.
Former England men's striker Wright described the playing surface as a "disgrace" on social media.
The pitch at the home of Real Madrid men's reserves deteriorated at a rapid rate, making free-flowing football difficult for both sides.
However, Arsenal did have their chances.
At 0-0 Stina Blackstenius forced Misa Rodriguez into a flying save after combining with Alessia Russo before Beth Mead went close from outside the box at the end of the first half.
Danish referee Frida Klarlund waved away Arsenal appeals for a second-half penalty after a challenge by Maria Mendez on substitute Chloe Kelly, before Real Madrid doubled their lead through substitute Athenea del Castillo after an assist by ex-Gunners player Caroline Weir.
The return leg takes place at Emirates Stadium on 26 March with the winners facing Bayern Munich or Lyon in the semi-finals.