Tsitsipas began playing low-level ITF Futures events in Greece in 2013 shortly after turning 15, not long after he started competing on the junior tour. He qualified for his first event on the ATP Challenger Tour at the Burnie International in early 2015 while still 16 years old, but lost his only main draw match to Benjamin Mitchell. Tsitsipas won his first Futures title later that year and would go on to win a total of eleven such titles, five in singles and six in doubles, through the end of 2016. He also won his first Challenger match near the end of 2015 in Mohammedia in Morocco. Tsitsipas returned to Morocco a year later and reached his first two Challenger finals in back-to-back weeks at Mohammedia and Casablanca. This success in Africa helped him crack the top 200 later that October. Towards the end of that month, Tsitsipas was granted a qualifying wild card into the Swiss Indoors in Basel, his first ATP Tour appearance. He defeated Rajeev Ram in the opening round, but was unable to qualify after a loss to Robin Haase.