Rio 2016 champions Brazil were held 0-0 by Cote d’Ivoire in Olympic football on Sunday while Egypt and South Africa lost to Argentina and France respectively.
Germany, France and Spain also claimed first victories, and hosts Japan are the only side with the maximum points.
Coming off an opening 4-2 win over the Germans in a rematch of the Rio final from five years ago, Brazil found no opening against their African opponents.
They even had Douglas Luiz sent off in the 14th minute.
Cote d’Ivoire lost Eboue Kouassi with 10 minutes left in the game in Group D which both sides lead on four points apiece.
Germany follow on three after a tense 3-2 victory over Saudi Arabia, with Felix Uduokhai scoring a 75th-minute winner although team-mate Amos Pieper was sent off eight minutes earlier.
Japan meanwhile improved to maximum six points in Group A from a 2-1 win against 10-man 2012 gold medallists Mexico who have three points.
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Mexico are just as France who came from behind three times in a late 4-3 win over South Africa.
Teji Savanier scored a stoppage-time winner after Andre-Pierre Gignac levelled three times for a hat-trick he completed in the 86th minute.
Rigobert Rivas gave Honduras a late 3-2 victory against New Zealand in Group B where all four teams have three points.
South Korea won the other game 4-0 against Romania, with a brace from Valencia’s Lee Kang In.
Spain moved top of Group C with four points past Australia from a 1-0 against them, thanks to Mikel Oyazabal’s 81st-minute winner.
They finish on Wednesday against Argentina who got their first points in a 1-0 against Egypt.