A patient Großschartner stayed with his more aggressive companions in the weather-shortened 164.1km Queen stage from Bursa to Kartepe. before riding on to a solo victory and into the leader's jersey.
Riding in cold, snowy and mountainous conditions suited to a man from Austria, Großschartner finished nine seconds ahead of Valerio Conti (UAE-Team Emirates) and Merhawi Kudus (Astana).
“I am speechless, this is the first WorldTour victory in my career and my first leader’s jersey as well," Großschartner said.
"I want to say thank you to the whole team for their amazing job today and during the whole week.
"In the finale, Michael Schwarzmann was so strong and helped position me for the final ascent. When we were just four riders at the front, I knew I could go for a stage win.
"Of course, I was careful as Kudus attacked, but then I went all in and was so focused, even if I couldn’t feel my hands I just kept going.
"I am more than happy with today’s win, to wear the leader’s jersey means a lot to me and of course I want to bring it home tomorrow, for me but also for BORA-hansgrohe."
Right from the first serious rises, several riders lost contact with only a select group heading into the final five kilometres.
Conti was the first rider to make a serious move, followed by an attack from 19-year-old phenom Remco Evenepol (Deceuninck-Quick Step).
Großschartner, however, kept his focus during the unrelenting grind, following all the moves to remain in control of the stage before attacking with two kilometres to go.
Kudus was the only rider in the group with the legs to follow before launching his own counter-attack. But Großschartner kept his head and pace, trailing Kudus by just a few seconds.
At the one-kilometre kite Großschartner closed the gap before making the decisive move with 300 metres to go. Kudus had nothing left with which to counter and Großschartner took a stage win.
Conti also kept to his pace after he was dropped. He stayed with Evenepol before finding renewed vigour to pass a depleted Kudus a metre from the finish to take second.
With only a flat sixth stage from 172.4km Sakarya to Istanbul suited to the sprinters left to contest, Großschartner only has to stay upright to claim the overall victory.