Viktor Gyökeres set up Noni Madueke to make it 1-0 in the ninth minute, receiving the ball before sending it through to Madueke.
In the 38th minute, Gyökeres scored Arsenal’s second.
He played the ball to Mikel Merino and got it back before carrying it forward and slotting it inside the far post.
Gyökeres had not scored in the league during the autumn, having been allowed just one start, but had nevertheless been involved in five goals in his last five competitive matches: two goals and three assists.
Slavia Prague pulled one back late on, but Arsenal held on to win 2-1. The Gunners, who reached the final last season but lost to Paris Saint-Germain, have started the Champions League league phase with three wins and one draw.
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