The Prema driver saved his best until the final moments of the 45-minute session, posting an impressive 1m22.423s effort, which proved 0.523s faster than nearest rival Dan Ticktum, who also starred late on.
After three interruptions a flurry of fast times came in the closing stages, with Juri Vips (Hitech Grand Prix) fastest heading into the last five minutes. However, he would have to settle for third just ahead of Felipe Drugovich (UNI Virtuosi) and Bahrain race winner Oscar Piastri (Prema).
Roy Nissany was the first driver to post a timed lap in the bright and sunny conditions that greeted the drivers.
The DAMS driver’s 1m35.534s came just moments before the session was halted after 10 minutes when Trident’s Marino Sato came to halt shortly after exiting the pit lane.
Campos Racing’s Ralph Boschung significantly lowered the benchmark with a 1m27.258s posted shortly after the session restarted.
Times continued to tumble as Drugovich briefly put his UNI-Virtuosi on top before Bochung responded with a 1m24.742s effort.
Drugovich continued his fast start to the session dipping a tenth underneath Boschung’s time at the top of the time sheets.
While Boschung was flying high, the same couldn’t be said of his teammate Gianluca Petecof, who suffered a spectacular engine failure on the run up the hill from St Devote. Clouds of white smoke bellowed from the car before flames emerged from the rear of the Campos, necessitating a second red flag.
The session resumed with 19 minutes remaining with Drugovich heading Boschung, Ticktum and Nissany but the action only lasted five minutes when officials deployed a Virtual Safety Car period to recover the Trident of Bent Visceral, who ran wide and stopped after nudging the barriers at Rascasse.
The final 10 minutes saw several improvements as Vips became the first man to dip under the 1m24s bracket. He went on to improve again with another impressive effort having a further six tenths off his time, before Shwartzman came to the fore to ultimately top the times.
After showing strong pace throughout, Boschung ended up sixth ahead of Liam Lawson (Hitech Grand Prix) and countryman Marcus Armstrong (DAMS).
Championship leader Guanyu Zhou was ninth while Nissany rounded out the top 10.
F2 returnee Jack Aitken was 13th fastest for HWA as he stands in for Matteo Nannini.
The F2 field will return to the track later today for qualifying which will be split into two sessions featuring 11 cars each, beginning at 11:20 GMT.
Cars with even numbers will take part in the first 16 minute Group A session while odd numbered cars will participate in the second Group B session.
The results from qualifying will set the grid for Saturday’s feature race while the top 10 will be reversed to form the grid for Friday’s opening sprint race.