Dominic Thiem became the inaugural champion when Teymuraz Gabashvili retired 7–6, 5–1.
Teymuraz Gabashvili was the defending champion but chose not to participate.
Gilles Simon was the defending champion, but lost in the first round to Teymuraz Gabashvili.
Dominic Thiem (] ; born 3 September 1993) is an Austrian professional tennis player who has an ATP high ranking of world No. 7 which he first achieved on 6 June 2016.
 He has won eight singles titles on the ATP Tour.
Teymuraz Gabashvili was the defending champion but decided not to participate.
Teymuraz Gabashvili was the defending champion, but decided not to defend his title.
Teymuraz Gabashvili was the defending champion; however, he chose not to play this year.
Mikhail Elgin and Teymuraz Gabashvili were the defending champions, but Gabashvili chose not to compete this year.
 Elgin played alongside Alexander Kudryavtsev and lost in the first round to Frank Moser and Alexander Satschko.
Teymuraz Gabashvili was the defending champion, but decided not to compete.
Nino Serdarušić (born 13 December 1996) is a Croatian tennis player.
 Serdarušić had a career high junior ranking of 21, and partnering Petros Chrysochos, made the doubles semifinals of the 2014 Wimbledon Championships boys' doubles.
 He made his ATP main draw debut at the 2014 ATP Vegeta Croatia Open Umag in the doubles event, partnering Dino Marcan, losing in the first round to the second seeds Pablo Cuevas and Horacio Zeballos in three sets.
 In 2016, he made his first appearance in an ATP singles final - also in the Croatia Open - losing in straight sets to Teymuraz Gabashvili.

Question: How many singles titles on the ATP tour have been won by the person who replaced Teymuraz Gabashvili as inaugural champion?
Answer: eight