Marco Asensio and Francisco "Isco" Alarcon were the big winners in a match that had little at stake for Real Madrid.
Vinicius played well throughout and claimed his second goal for Madrid with a shot from inside the area in the 75th minute at Santiago Bernabeu Stadium.
Arsenal and Chelsea have joined a handful of European giants in the hopes of signing Real Madrid midfielder Isco during the January transfer window, according to reports. When I play with Asensio, we link up and have exchanged three passes, but it's the same with the other players too.
A much-changed Real Madrid put six goals past Melilla in the Copa del Rey in midweek
He said: "Everyone thinks they should start, otherwise they would not be here".
Ballon' d'Or victor Luka Modric, Gareth Bale, Sergio Ramos, Raphael Varane, Karim Benzema and Thibaut Courtois are all expected to return to Solari's starting XI after sitting it out in midweek. I got very sad because he failed to score before the break what could have been a great goal.
He returned to the first XI for the formality of Thursday's second-leg tie against third-tier opponents, with Madrid already holding a 4-0 first-leg advantage. It was the third win for Athletic in 16 matches this season, and the team's first match since Argentine coach Eduardo Berizzo was sacked.
Wednesday night saw Barcelona, Atletico Madrid, Sevilla and Valencia all book their places in the last 16 with the draw to be made on Friday.