The France international netted his fourth double of the season, three days after a brace against West Ham United, to help the Gunners advance to the fifth round.
Giroud scored just once in his first 10 appearances since arriving at the Emirates Stadium from Montpellier in the summer.
However, after four goals in a week, Wenger has applauded the 26-year-old for his recent improvements.
The Arsenal boss said: "He has scored four goals this week and that will give him confidence from the slow start he had. He is getting stronger - he's a fighter.
"He scored two goals but he had four or five chances - that is very pleasing. He also wins the ball in the air, which for us is unusual."
Giroud has scored 13 goals in 32 Gunners appearances this term.