Arsenal conceded a 91st-minute equaliser against Vitoria Guimaraes in Portugal to draw this Europa League tie 1-1.
Shkodran Mustafi had provided the Gunners with the breakthrough with an unmarked header from a Nicolas Pepe free-kick with 10 minutes to go.
But Vitoria came to life in the closing stages and former Spurs man Marcus Edwards' cross from the right caused confusion in the Arsenal defence, allowing Duarte to equalise with a scissor-kick.
The result was Arsenal's fourth consecutive draw in all competitions in a turbulent week that saw Granit Xhaka stripped of the captaincy.
Gunners boss Unai Emery said, "The players worked and tried. We came really close to the win. Our objective in this competition is to come first in the group - at the moment we are.
"We tried but they are a very competitive team. What was very important for us today was to be strong defensively and I thought we did that. It was 1-1 but I think we were defensively better.
"Offensively against this team it is not easy to create chances. Overall, it is not good because we want to win but for the table we are first and that is our target."
