French giants Lyon last won this competition in 2022, under current Chelsea manager Sonia Bompastor, but they will be desperate to return to the top under their new owner, Michele Kang, who also owns London City Lionesses and US-based Washington Spirit.
The wealthy American businesswoman was at Meadow Park and would have been thankful to see her side avoid further damage than the concession of Russo's goal amid the early Arsenal pressure.
And Dumornay soon seized control of the match for the visitors.
The 22-year-old was the player furthest forward, applying pressure to the Arsenal backline, when Van Domselaar fluffed a kick and presented a golden opportunity.
Dumornay's running and energy was a problem for the home side all evening, but her finesse was on show too.
The midfielder produced a classy finish from the edge of the area to give Lyon the lead, and her impact on the match did not end there.
She was at the heart of Lyon's attacks and her passes into space behind the Arsenal backline meant that the wingers were always a threat.
There was a chance of a hat-trick for Dumornay before half-time as she flashed another dangerous shot just wide from the edge of the box.
She did not get that third goal but it did not matter as the away side headed away from north London with three points.
