Lyon begin Champions League defence with narrow victory
Just two minutes remained when Melvine Malard set up Kumagai to score from close range in Turin and give Lyon a narrow advantage for the second leg of their last-32 tie.
Winners of the Champions League in each of the last five seasons, Lyon had earlier come from behind twice against the Italian champions, with Swedish international Lina Hurtig's opener for Juve being cancelled out by a Wendie Renard penalty.
Kadeisha Buchanan's own goal put Juve back in front before half-time, but Malard came off the bench to equalise before setting up the winner.
The second leg will be played next Tuesday.
However, their hegemony at home and abroad now appears under threat, with Paris Saint-Germain currently top in France and the departure of England right-back Lucy Bronze to Manchester City pointing to the emerging competition elsewhere in Europe.
She has been replaced by Australia's Ellie Carpenter, but Lyon are still missing 2018 Ballon d'Or winner Ada Hegerberg as she recovers from a tibia stress fracture.
Wolfsburg lost their star Danish forward Pernille Harder to Chelsea after last season's final, and she scored for the English WSL champions in their 5-0 victory away to Benfica.
Fran Kirby scored twice, with Millie Bright and Bethany England also on target against a Benfica team who finished with 10 players after the sending-off of Nigeria's Christy Ucheibe.
Goals from Georgia Stanway and US World Cup winner Sam Mewis allowed Manchester City to come back and win 2-1 away to Gothenburg in Sweden.
Jennifer Hermoso, Nigeria's Asisat Oshoala and Dutch star Lieke Martens all found the net for Barcelona in their 4-1 win away to PSV Eindhoven.