Umag - Local wildcardupset top-seeded David Goffin 7-5, 6-3 to advance to the Croatia Open semi-finals on Friday.
Before this tournament, Dodig had not recorded a singles win on the main tour since June 2016 because he'd been focusing on doubles.
The Croatian, ranked 412th in singles and 7th in doubles, is seeking his second career singles title after winning in Zagreb in 2011.
For the 14th-ranked Goffin, the tournament marked his return from an ankle injury at the French Open, which forced him to miss the entire grass season.
Dodig next plays defending champion Fabio Fognini of Italy or lucky loser Andrey Rublev of Russia.
Also, Alessandro Giannessi of Italy made the semis by defeating Rogerio Dutra Silva of Brazil 6-7 (3), 6-2, 7-5.
Results from the ATP tournament in Umag on Friday (x denotes seeding):
Quarter-finals
Ivan Dodig (CRO) bt David Goffin (BEL x1) 7-5, 6-3
Andrey Rublev (RUS) bt Fabio Fognini (ITA x3) 6-7 (5/7), 6-2, 7-6 (7/2)
Paolo Lorenzi (ITA x4) bt Jiri Vesely (CZE x8) 1-6, 7-5, 6-3
Alessandro Giannessi (ITA) bt Rogrio Dutra Silva (BRA) 6-7 (3/7), 6-2, 7-5