The Briton was knocked out in Q2 and qualified in 13th place, but will start from 16th position after being hit with a penalty for overtaking under red-flag conditions on Friday.
Button finished six places behind McLaren team-mate Sergio Perez and said he expected much more.
"I haven't got a clue," said Button when asked about his lack of pace. "It's strange, because all weekend I've been very quick.
"I didn't go quick enough, basically. I don't know why."
He admitted the conditions, warmer and windier than on Friday, had made for a strange session.
"It's very weird, especially in Q1 when you see [Valtteri] Bottas quickest and his team-mate out. I don't get it," he said.
Perez will start from seventh position, the Mexican bouncing back from a difficult Friday during which he struggled with a car suffering a mechanical problem that was discovered overnight.
"It was better than expected. I'm happy to see the car has improved. We did a good job," said Perez.
"Tomorrow I have nothing to lose and I hope to give the fans a great race.
"Unfortunately the work we did yesterday is not going to be useful because the car had a problem, so it's going to be interesting to see what I can do."