George Russell started life as an official Mercedes junior in style by topping day one of GP3 pre-season testing at Estoril.
The ART Grand Prix driver set a 1m27.606s in the afternoon, almost eight hundreths quicker than team-mate Nirei Fukuzumi.
The morning session was disrupted by wet weather, meaning nobody set representative times.
Raoul Hyman, testing with Campos with a view to securing a race deal, switched to slick tyres in the closing stages and ended up five seconds quicker than the rest, who were led by Red Bull Junior Niko Kari.
In the quicker afternoon sessions the times dropped continuously, and it was a relatively late effort that put Russell on top.
Hyman did well to go third quickest, ahead of the third ART man Anthoine Hubert, Jenzer?s Arjun Maini and Ferrari junior Giuliano Alesi of Trident.
The absence of race-winning team Korainen meant 19 drivers featured in the first day of the test, a reduction from the numbers seen during last year.
The day’s running was the first collectively with the new DRS system that GP3 has introduced for 2017.