Heavy rain over the weekend forced the tournament into a second week, but Konjuh was unruffled by the change in schedule, overcoming a disastrous start to triumph, 1-6, 6-4, 6-2.
After winning twice on Sunday, Konjuh looked understandably weary-legged early on as she struggled to get to grips with Niculescu's unorthodox game. This was the first set the 17-year-old had dropped all week and provided the wake up call required.
Once into her stride there was no stopping the young Croat, who romped home to become the youngest player to lift a WTA title since a 15-year-old Tamira Paszek triumphed at Portoroz in 2006.
"The first set wasn't going my way but I had to stay calm. I just knew that my game was going to come and I did it much better in the second set. I'm really glad to get that win today," Konjuh said. "She's an uncomfortable player to play against, especially on grass with that many slices. It's so frustrating. But she has that experience and she took the first set because I wasn't ready for it."
"It means a lot, especially because it's the first year for you guys here. It feels great, I didn't expect it. I came here two days before to acclimatize on grass, and after five matches I've won the tournament, so it feels great. I will remember that - it's going to hold a special place in my heart, this tournament."
Konjuh enjoyed a standout junior career, winning the Australian and US Open titles, and has not taken long to replicate this success in the senior ranks. Last year she reached a semifinal in Istanbul and a quarterfinal in Osaka and is rapidly closing in on a Top 50 place.