Gerardo Martino's side went in two goals down at the break, and Pique said that the opening 45 minutes simply weren't good enough.
"We played a horrible first half," Pique told reporters.
"There is no excuse - it was a disaster. What happened in the first half can't happen again. The attitude wasn't right; the whole team know that."
Despite the loss, Barca have still qualified from Group H.