Defender Joan Capdevila has no doubt that Spain have now completely recovered from the psychological setback of the shock defeat to Switzerland.
The European champions were stunned in their opening game of the World Cup as the pre-tournament favourites lost 1-0 to the Swiss in Durban.
Spain have since booked a meeting with rivals Portugal in the last 16 after they defeated Honduras and Chile in Group H.
But Vicente del Bosque's side are still to find their stylish top gear and it has been suggested they are still reeling from the upset against Switzerland, which was only a second defeat in 49 matches.
Villarreal left-back Capdevila, though, insists that Spain are a strong unit, saying: "We've shown we've overcome the blow of the first game, and now the squad is more united than ever, with morale pretty good.
"We've done well to be able to win and get through as group winners. Now we are playing Portugal, which will be a very nice tie."
He added on the Spanish football federation's official website: "We've recovered from the psychological blow, which was the hardest thing to do.
"We didn't have any doubts about our play or our qualification, but it was crucial for us to recover mentally and now we're strong."
Capdevila also believes that Spain are blessed with a wealth of attacking talent, despite a slightly disappointing return of four goals from three matches.
"It's great to play with players like (David) Villa, (Fernando) Torres, (Fernando) Llorente. We have some of the best strikers in the world," he said.