The 26-year-old attacker admitted that Slaven Bilic's men posed his side a lot of problems, while stressing he has no preference for an opponent for their last eight clash
The defending champions had to wait until Jesus Navas' 88th-minute winner to seal their passage to the last eight, but finished top of Group C and will face either France, England or Ukraine.
"Those are all great teams and we will have to wait for [Tuesday] to learn who we will face," he told reporters after the game.
"Whoever we face will always be hard to beat."
Slaven Bilic's side had been laying siege to Iker Casillas' goal for prolonged periods of the second half, and defeat would have signalled a surprise early exit from the tournament.
But Silva was not surprised that they had to work hard for victory.
"Every match is complicated. We were able to win and we are happy for that," he added.
"The first half was complicated because they defended too deep, but as the game wore on, they opened up more.
"We knew it would be tough, but the most important thing is that we are through."