It was a bad day at the office for the Red and Whites as they slumped to a 3-0 reversal at Estadio Municipal de Anoeta.
Willian Jose opened the scoring in the 27th minute, before Juanmi added a second half double to condemn Diego Someone's men to their fourth league loss of the campaign.
“We have to apologize to the fans," Partey said.
"We must forget about this match and think about the next.
"They played well and took advantage of their chances.
"We have to pick ourselves up and keep fighting.
“We want to win all the matches that remain and see what happens.
"We have a philosophy that takes us game-by-game.
"We have to go game-by-game and think about our game against Betis."
Partey played for 75 minutes before being replaced by Gabi.
It was his 29th appearance and 24th start in La Liga this term.