The first leg in Spain was settled by the attacker with a curling free-kick in the second-half.
It was the 19-year-old's 19th goal in all competitions since he broke into the first team over a year ago, but it was his first from outside the box.
1 - Marcus Rashford's strike was his 19th for @ManUtd in all competitions, but his first from outside the box. Lash.— OptaJoe (@OptaJoe) May 4, 2017
After scoring against Chelsea and Sunderland last month in the Premier League, Rashford fired United into the last four of the Europa League with an assist and an extra-time goal in his side's second-leg win over Anderlecht.
The attacker has impressed since making his debut in United's Europa League win over Midtjylland last season and is their second highest goalscorer this season, behind the injured Zlatan Ibrahimovic.