Mead and Russo made their contributions in the final 33 minutes in Lisbon, after the Gunners had lost 2-1 at home to Lyon last week.
Benfica are 15th in the 18-team table having suffered a second straight defeat.
Elsewhere, Paris Saint-Germain are also winless after two games having lost 2-1 in the French capital to Real Madrid.
The major drama came in Bavaria as Germany forward Lea Schueller netted after 95 minutes in Bayern Munich’s 2-1 win over Juventus.
Earlier, experienced Sweden winger Fridolina Rolfo scored as Manchester United edged Atletico Madrid 1-0 to maintain their perfect start to the season.
Rolfo, 31, volleyed home in the first half after the English club beat Valerenga last week and are fourth in the table.
Atleti are ninth in the 18-team league phase, having hammered St Poelten 6-0 eight days ago.
Both sides finished with 10 players in the Spanish capital after United’s Netherlands defender Dominique Janssen and the hosts’ Spanish midfielder Alexia Fernandez were shown red cards.
Barcelona are top of the standings, thanks to their 4-0 victory at Roma while Chelsea hammered Paris FC by the same scoreline on Wednesday. (AFP)
