The Spanish winger stressed that Los Rojiblancos showed character at Anfield.
"[The game at] Liverpool was incredible," Vitolo said.
"We were on the ropes.
"We qualified thanks to [Marcos] Llorente.
"It was unique and memorable in a mythical stadium.
"On top of that, we did it by winning the tie and qualifying.
"You can see the greatness of this club."