Parreira had anticipated a long, frustrating wait to break down a Bolivia team fielding four defenders and four defensive midfielders in their World Cup qualifier.
Instead, Ronaldo scored after 55 seconds to set the world champions Brazil on their way to an easy 3-1 win.
"I've no doubt that the goal in the first minute changed the face of the game,"
"If we'd taken a long time to score, the crowd could have become irritated and the game could have got complicated."
Brazil raced to a 3-0 lead by halftime but failed to add to the total in the second half and allowed their opponents to pull one goal back. But Parreira denied his team had let up.
"We missed nine good chances in the second half," he said. "We could have opened up a good goal difference."
The world champions lead the South American World Cup qualifying group with 16 points from eight games. Bolivia are bottom on six points.
