With both sides competing in a major European semi-final for the first time in their respective histories, the opening stages were understandably cagey in Madrid.
Ben Chilwell fired a speculative long-range effort over for the visitors, while at the other end, Alemao was unable to direct a good headed chance on target.
Strasbourg looked to up the ante, with Gary O’Neil’s side seeing plenty of the ball in the final third, but Rayo remained typically resolute at the back, having previously kept a first-half clean sheet in five of their six European home games this term.
Encouraged by their solid defence, Los Franjirrojos probed for a breakthrough themselves, as left-back Pep Chavarria dragged a low effort wide of the far post.
That was the hosts’ best opportunity of the half, with Strasbourg wasting a promising chance of their own on the stroke of half-time through captain Emmanuel Emegha, who volleyed wastefully over the bar from 12 yards.
Having tasted defeat just twice on home soil since the start of October (W10, D7), Rayo came flying out of the blocks at the start of the second period, and their attacking intent was rewarded in the 54th minute with an opening goal.
Isi Palazon’s outswinging corner was perfect for Alemao, who directed a superb glancing header into the far corner beyond Mike Penders for his third strike in this year’s competition.
Keen to build on their lead, the hosts continued to stamp their authority on proceedings, with Florian Lejeune seeing a header smartly saved by Penders before Ilias Akhomach drilled a low strike narrowly wide.
Strasbourg briefly threatened at the other end when Andrew Omobamidele failed to convert from close range, but the visitors were soon indebted to Penders again, as the Chelsea loanee thwarted a free header from Lejeune.
That proved to be the last meaningful chance of the contest, with Le Racing holding firm to avoid further damage, setting up a fascinating return leg in France next week for a spot in the final.
Flashscore Man of the Match: Isi Palazon (Rayo Vallecano)
See the match stats on Flashscore.
