Russo's late strike came in front of over 40,000 fans at the Emirates Stadium, sealing a remarkable comeback to inflict Arsenal's first defeat of the 2022/23 campaign.
The hosts were five minutes away from a seventh consecutive victory after second-half goals from Frida Maanum and Laura Wienroither cancelled out Ella Toone's first-half opener.
Millie Turner equalised with five minutes to go, before Russo's strike proved to be a dramatic winner in injury-time.
Speaking to Sky Sports after the game, Russo said: "The whole second half was a whirlwind, we come to these games and want to test ourselves and come away with three points so we're really happy.