Arsenal's record signing Nicolas Pepe stepped from the bench and scored two sumptuous late freekicks to hand the Gunners a 3-2 comeback win over Vitoria Guimaraes.
Unai Emery made 10 changes from the side that lost to Sheffield United on Monday night, but Arsenal were slow starters and fell behind after eight minutes.
Former Tottenham Hotspur youngster Marcus Edwards, showed clever footwork and fired past Emiliano Martinez to hand the Portuguese side the lead.
Gabriel Martinelli equalised before Bruno Duarte fired the away side back in front.
Arsenal, with Alexandre Lacazette leading the line in the absence of the rested Pierre-Emerick Aubameyang struggled for rhythm in attack.
Then Pepe arrived and with two sweet strikes of his left foot, they continued their 100 percent record in the Europa League this term.