Inexperienced Gunners striker Yaya Sanogo, who was handed a starting spot after Danny Welbeck suffered a late injury, broke the deadlock with a clinical finish in the second minute.
The Arsenal youngster wasted the chance to bag his second of the night minutes later, while Gunners centurion Alex Oxlade-Chamberlain hit the crossbar early in the second half.
But £35m summer signing Sanchez sealed three points with a powerful finish past Roman Weidenfeller with 33 minutes remaining at The Emirates, booking the north London club’s place in the last 16.
“[Sanchez showed] unbelievable fighting spirit and his class as well. He is a mixture of talent and desire – that is what you expect from top-level players,” Wenger told Sky Sports.
On Sanogo’s performance, Wenger continued: “I liked what he did tonight because we decided to go long on him. He protected the ball well. His combination play was good with Cazorla.”
Wenger was thrilled with Arsenal’s defensive performance, too, as the north London side limited Dortmund to half chances in north London.
“We defended well together. It was a similar game to Saturday but we focused really well not to give any chances away. Overall, it was a committed game and maybe defensively we were better tonight,” Wenger added.
“We are a team that likes to go forward. Sometimes when you feel like you dominated a game, you are a victim of that and forget to take the precaution to defend well. We learn from the games, as well.”
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