Netherlands, ranked No. 4 in the world, routed Zambia 10-3 in their Olympic opener with Miedema scoring four goals.
Brazil beat China 5-0 in its opener. Marta had a pair of goals, becoming the first player to score in five straight Olympics.
Marta's goal brought her to 13 at Olympics, which is one behind the all-time record held by Brazil teammate Christiane, who is not in the 2020 squad, but the Orlando Pride forward said she is only focused on team success.
"Our objective is to think of the collective," Marta told Brazil's Globo TV after the match. "Scoring goals is part of our job, but always while thinking about the collective [goal].
"Records always happen naturally in my life, it's never been forced. If I have to score one, two goals to help my team, then it's normal."
Brazil are coached by former U.S. and Sweden coach Pia Sundhage, who won gold with the Americans at the 2012 London Games.
Earlier, Zambia and China had drawn 4-4 in another epic match in Group F.