Thiem was beaten 6-3, 6-2 by qualifier Ramanathan on Centre Court with the Indian advancing to the quarterfinals in Turkey.
“I just gave it my best and was serving well out there. Two or three points can often make the difference on grass,” Ramanathan said. “It’s a good start for my career, but it’s just a start. Hopefully I can keep it going.”
Third seed Fernando Verdasco is safely through to the last eight following a 6-3, 6-4 win over Steve Darcis. He faces Adrian Mannarino next, after the Frenchman defeated Mohamed Safwat in straight sets.
Martin Klizan was forced to retire injured in the first set of his clash with Marshel Ilhan, who will play Daniel Altmaier in the next round after the German beat Victor Estrella Burgos 7-5, 6-7 (8), 7-6 (5).
Elsewhere, Janko Tipsarevic beat Lloyd Harris 7-5, 6-3 while Andreas Seppi saw off qualifier Kamil Majchrzak 6-2, 7-6 (1). Marcos Baghdatis is also through following a 6-4, 3-6, 7-5 win against Carlos Berlocq.