The 25-year-old fired the Gunners into the lead at the Liberty Stadium in the 63rd minute when he turned home Danny Welbeck’s low pass.
However, the Swans fought back thanks to Gylfi Sigurdsson’s free-kick and sealed victory when Bafetimbi Gomis headed in a winner in the 78th minute in South Wales.
Sanchez’s strike was his eighth Premier League goal in 10 games this term, but Wenger said: “He scored but I think he didn’t have the best game today.”
Wenger conceded that the defeat marked the end of a disappointing week for his side after they squandered a three-goal lead against Anderlecht on Tuesday night.
“We had a very disappointing week and considering the performances we produced and the end result we got, it’s very disappointing,” he continued.
“We were 3-0 up against Anderlecht and 1-0 up today. In the end we’ve lost two points against Anderlecht and three points today.
“It’s very, very disappointing because we have to be capable of winning the game once we’re a goal up.”
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