With conditions constantly improving at the Saudi Arabian street circuit it was the final efforts which proved crucial as Nato jumped to the top of the times with a 1m13.584s as the chequered flag was shown.
Moments earlier Maserati MSG’s Guenther had gone fastest, usurping reigning champion Jake Dennis who had lingered towards the top of the times throughout the 30-minute session.
The Andretti driver became the first driver to dip below the 1m16s mark, posting a 1m15.710s inside the first 10 minutes before lowering his personal best to a 1m15.067s with his next effort.
It left the Briton more than a second clear of Sam Bird’s McLaren in second with Bird’s team-mate Jake Hughes third.
Pascal Wehrlein became the second driver to post a time below the 1m16s barrier, setting a 1m15.706s which was still some 0.639s behind Dennis at the head of the field.
Approaching the halfway point, Wehrlein’s Porsche team-mate Antonio Felix da Costa moved into second ahead of Robin Frijns, the Envision driver having taken to the Turn 18 run-off in the opening minutes.
Nick Cassidy posted a 1m14.723s to go top but the Jaguar driver’s effort was immediately beaten by the Mahindra duo of Edoardo Mortara and Nyck de Vries.
Mortara’s 1m14.438s stood as the best time until there was only nine minutes left before Dennis vaulted back to the top with a 1m13.687s and only failed to improve on his next effort due to traffic.
Source: Autosport