Many say the Spanish Liga is becoming worse than the Scottish Premier League for competitiveness.
But Guardiola says: "It was a very difficult game.
"I was very impressed with Villarreal in every sense. They play really, really good football.
"The rival was immense. They are a top team. They play so, so well. We have beaten one of the best teams in the world."
"Put them in the Premiership and they would cause problems to the big teams," he said.