The German posted the quickest time with his final run, a 1m29.269s putting him to the top of the times and just 0.007s clear of Jaguar’s Mitch Evans.
Gunther had earlier headed the times approaching the 10-minute mark in the session with a 1m31.002s, before Evans became the first driver to go below the 1m31s barrier.
The Kiwi posted a 1m30.784s to put him fastest as McLaren’s Jake Hughes moved into second just 0.034s in arrears, as Gunther also improved to a 1m30.885s in third.
Approaching the halfway point of the 30-minute session Envision Racing’s Sebastien Buemi moved to the head of the times with a 1m29.849s, nearly a full second clear of Evans’ earlier benchmark, but was quickly bested by Sacha Fenestraz’s 1m29.788s.
The Nissan driver remained fastest until nearly the final 10 minutes as Buemi moved back to the top of the timing screens, improving his personal best to a 1m29.679s and 0.109s clear of Fenestraz.
Evans found further performance with a 1m29.584s as drivers continued to lower their lap times in the final five minutes.
Andretti Autosport’s Jake Dennis and Evans again occupied the top of the times in the final moments, before Gunther finished fastest with his final effort.
Behind Dennis in third, NIO 333’s Sergio Sette Camara claimed fourth ahead of DS Penske’s Stoffel Vandoorne and Evans’ team-mate Sam Bird, with Buemi occupying seventh.
Source: Autosport