Karatsev made his ATP main draw debut at the 2013 St. Petersburg Open where he received entry to the main draw as a wildcard entrant. In the first round he lost to compatriot and second seed Mikhail Youzhny, 7–6(7–5), 2–6, 2–6. In the doubles event, he partnered Dmitry Tursunov where they reached the semifinals, losing to Dominic Inglot and Denis Istomin, 4–6, 7–5, [9–11].