Willian Jose had La Real ahead before Jordi Alba and Frenkie De Jong struck for the Catalans.
Koeman said, "It was the best first half we've played, we were very good with the ball and pressed well. We had chances. It could have been more than 2-1 at the break. The second half was complicated because of the opponent's quality. It was a really intense game. We created chances, but La Real had some, too."
"You cannot control a game for 90 minutes. And when you have to defend, you defend. The effort they put in was impressive. On attitude, the win was deserved."
He added: "The system depends on the opponent. Sometimes you need one pivot and two interiors. With Pedri and De Jong, you can do the two things. In football these days there's a lot of movement. You also have to react to the change of positions rivals like La Real make."