The first goal came from friendly fire, with the feet of Pervis Estopinan, who scored in the 53rd minute. Two minutes later, Senegalese Sadio Mane added the second goal after a smart pass from the Egyptian Mohamed Salah.
The return match between the two teams will take place at La Ceramica Stadium next Tuesday.
It is noteworthy that the winner of this match will meet the winner of the match between Real Madrid and Manchester City, next Wednesday.
Villarreal qualified for the semi-finals of the European Champions for the first time in 16 years, after eliminating Italian Juventus and Bayern Munich. As for Liverpool, they booked their place in the semi-finals after winning the first leg 3-1 away from Benfica, and drawing 3-3 in the second leg.