Real Madrid manager Carlo Ancelotti hailed the impact made by Gareth Bale on the Welshman's return from a four-match absence with a calf injury.
The £85m summer signing, 24, played the full 90 minutes in Real's 2-0 Copa del Rey win over Osasuna at the Bernabeu.
Goals from France striker Karim Benzema and young forward Jese Rodriguez put Los Blancos in command of the last-16 tie ahead of next week's second leg.
"Bale played very well and was very dangerous," said Ancelotti.
Bale missed Real's entire pre-season programme as his world-record move from Tottenham was being completed, and he struggled with a foot injury on his arrival in Spain.
The Cardiff-born player made a goalscoring debut for Real against Villarreal in September, before scoring eight goals in seven games following a 2-1 defeat at arch-rivals Barcelona in October.
However, Bale had not played since 14 December before returning in Thursday's win against Osasuna.
"Everyone knows he had injury problems and he is a player that needs to be in optimal condition," added Ancelotti. "For that reason he played the whole game.
"In the second-half the game was more open and it suited him more, but we are all very happy with him."