Louis Deletraz pipped Ferrari Formula 1 junior Marcus Armstrong to lead the opening day of Formula 2 post-season testing in Abu Dhabi.
Deletraz, driving for Charouz Racing, improved to a 1m50.543s at the last moment to deny Armstrong's ART Grand Prix outfit a 1-2.
The French team led the way from Armstrong's Renault-backed squadmate and fellow F3 racer Christian Lundgaard - whose 2020 seat is yet to be confirmed - for most of the afternoon session.
Lundgaard's 1m50.923s was enough to put him 0.024s clear of Mick Schumacher's first-hour benchmark, which had allowed the Ferrari junior to lead Deletraz by just over a hundredth of a second heading into the mid-day break.
Armstrong found another half a tenth as qualifying simulations began in the final hour, only for a Mahaveer Raghunathan stoppage to bring out a red flag.
Once this was withdrawn, Armstrong improved further, only to be left a quarter of a second adrift by Deletraz's last-gasp effort.
Schumacher was fourth-fastest in the afternoon and took the spot in the overall classification, although his morning time ultimately stood as his best effort.
Nikita Mazepin, running for Carlin, made up the top five on the day, likewise courtesy of his opening-session effort as he logged no representative short-run efforts late on.
The same was true for Renault protege Guanyu Zhou, who ended up sixth overall.
DAMS driver Sean Gelael and HWA's 2020 signing Artem Markelov were the only two other drivers to lap within a second of Deletraz, albeit with both more than nine tenths adrift.
Luca Ghiotto (Trident) and Ferrari junior Callum Ilott (UNI-Virtuosi) made up the top 10, ahead of newcomers Pedro Piquet (Charouz) and ex-Red Bull junior Dan Ticktum - the latter confirmed at DAMS alongside Gelael for 2020.