Simeone insists they handled the pressure of the Rotterdam crowd for the 3-1 win.
He said: "Very happy for the footballers, they have been playing very important games.
"Today we knew it was a difficult game, how well they had played in Europe, but we interpreted it well with very good performances and collectively we played an important game for the club.
"We could have scored the third earlier, it's a shame we didn't have the efficiency at the end of the play, we left them alive, they made it 2-1 and everything started to move. But we made it 3-1.
"It is always important to finish as high as possible, to continue working, to rest because the game demanded a lot from us and to think about Sunday, which will be difficult.
"The rival that put the best pressure on us was Celtic in their field. Afterwards, I don't share the pressure we saw with Feyenoord at home so much. Today they tried but backed off. The team has Witsel, Hermoso, Koke, De Paul... the team has strength and generates it.
"We know our defects and we try to correct them. Great game from Riquelme, which many did not believe he would play, but he gave us a great performance with his strength."