Real Zaragoza grabbed the upper hand in their Copa del Rey fifth-round tie against Levante with a 1-0 win in Valencia.
Carlos Aranda scored the crucial goal in injury time after what was the visitors' only meaningful attack throughout the game.
Aranda latched onto Leo Franco's goal kick and sent a deft shot over the head of Levante goalkeeper Kaylor Navas to seal the win.
"It's an important win, but it's not decisive," Zaragoza coach Manolo Jimenez said. "The return leg will be difficult because Levante is a good road team."
Levante's strong form in La Liga, which has lifted them to sixth place, failed to resonate on Thursday and coach Juan Ignacio Martinez insists they didn't take the match lightly despite a number of noteable omissions.
"This is a different kind of competition [but] we fielded a team to compete tonight," Martinez said. "We are angry. We can't give the game away like that."
Elsewhere, Segunda Division side Las Palmas salvaged a 1-1 draw at home to high-flying Real Betis.
Ruben Castro scored the opener for Betis in the 67th minute, but Macauley Chrisantus equalised in the 84th minute to give the hosts hope of qualifying for the next round.
Information from the Press Association was used in this report