The French eked out a 94-90 victory against a relentless Japan in a heart-stopping overtime session, while Germany fought to beat Brazil 86-73 in Group B at the Pierre Mauroy Stadium.
Earlier on Tuesday, Canada stunned Australia 93-83, while Spain overcame a tricky test to defeat Greece 84-77 in the second round of men's basketball Group A action.
Some 27,000 mostly French fans went wild and then cautiously silent as the Japanese team overtook their Gallic rivals in an uncomfortably close cat-and-mouse match, which ultimately tipped toward France in a final five-minute tiebreaker.
"A win is a win, we're going to take it regardless," said French shooting guard Isaia Cordinier.
"I think this is the toughest competition in a while, maybe in history in terms of talent and level of basketball."
Germany started strongly against Brazil, leading by double digits in the first quarter before sputtering and allowing their South American rivals to tie the score at halftime.
German captain Dennis Schroder came to the rescue, scoring 20 points and providing the jolt necessary to rally his teammates to clinch the win.
In Group A, Greece's Giannis Antetokounmpo brought all his NBA experience as the Milwaukee Bucks small forward made 27 points, hitting 11 rebounds and three assists.
However, he was not prepared for Spain guard Sergio Llull, who combined with first-time Olympian and Memphis Grizzlies forward Santi Aldama to make 32 points.
Canada were up to the task of upsetting third-ranked Australia, who chased the North Americans throughout the game, but were unable to keep up.
Chicago Bulls point guard Josh Giddey led the Australians with 19 points, seven rebounds and six assists. But Canada's superior shooting, with the combined efforts of RJ Barrett and Shai Gilgeous-Alexander making 40 points.
On Wednesday, the winners of the USA-South Sudan match will also earn a spot in the quarter-finals.
The losers of that clash, along with Japan, Brazil, Puerto Rico and Serbia, will tussle for the remaining spots to make it to the next stage of the competition.
