A brace by each talented attacker ensures the tournament holders top Group B, and sets up a return fixture against Gerardo Martino's side.
"We had to win no matter what," Pato said. "We had find a good result and we did. We finish in first place - which was what we wanted - thanks also to the draw in the other match. Now the work starts and we forget all that happened. It is a new Copa America."
The game started well with both sides looking to attack, and in the early exchanges Ecuador held their own against the favourites.
Real Madrid target Neymar had the first chance of the game, picking the ball up and shooting from 25 yards out, only for his effort to be tipped over the top by Marcelo Elizaga.
Brazil had started to dominate possession and they took the lead on 28 minutes with a well worked goal. After a spell in the Ecuador half, Fenerbahce left back Andre Santos curled the ball into the opposition box, with Pato attacking at the near post and heading past a stationary Elizaga.
Brazil almost made it two on 36 minutes, as Maicon attacked down the right, cutting the ball back to Robinho, who shot from the edge of the box and saw his effort clip the left hand post.
However, from the resulting goal kick and against the run of play, Ecuador equalised. A long ball forward found Christian Benitez, who drew two men before feeding Felipe Caicedo at the edge of the box. The Levante attacker's effort had power but was straight at Julio Cesar, who fumbled the effort, letting it trickle into the Brazilian net.
The underdogs finished the half the stronger, and a Michael Arroyo effort stretched Inter keeper Cesar, who made amends for his earlier error with a good right handed stop, and the game went into the break all square.
Mano Menezes' team took the lead once more after 48 minutes, with Neymar getting his first goal for the tournament, firing home after being played through by playmaker Ganso.
However Ecuador refused to lie down, and another Caicedo strike from the edge of the penalty box made it 2-2 on 58 minutes, with Cesar's goalkeeping again under scrutiny as he was beaten at his near post.
Parity only lasted two minutes however, as Pato grabbed his brace after Eligaza spilled a ferocious Neymar shot into his path, and the Milan forward got to the rebound just ahead of Robinho.
The game ended as a contest on 71 minutes as great work by Maicon and Robinho down the right flank allowed the Inter full back to centre from the byline for Neymar to convert the fourth from six yards.
"We played well, we could at least have drawn the match," Caicedo said. "We lacked concentration at the end and gave Brazil too much space. We could not keep the same rhythm, and that hurt us in the rest of the game."
It could have been five in the dying seconds as Robinho slotted home, only for the goal to be chalked off.
Brazil now take on Paraguay on Sunday in the quarter finals, whilst Ecuador exit the tournament.
"It's going to be hard," Pato said of the quarters. "I'm sure that's going to be a different match. It is the quarterfinals. It is a new Copa America."
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