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Mansell started from eighth for the 22-lap encounter and climbed to fifth before the end of the opening lap.
He then picked his way up to second, where he shadowed race leader Luke Browning.
It’s a performance that comes after a difficult start to the season for the 19-year-old went from fourth on the reverse grid Sprint on Saturday to 14th by the chequered flag.
A set-up choice in the Australian’s ART Grand Prix entry saw Mansell struggle for grip, the team making a change ahead of the Feature that brought his car to life.
“You turned it around overnight. What a team, what a team,” Mansell said on the radio as he finished the race.
Off the start, pole sitter Dino Beganovic struggled to get away, the field doing well to avoid the crawling Prema as they steamed into the first corner.
That left Browning out front, the Williams Academy driver joined by Mansell on Lap 6.
The pair then ran nose to tail for the balance of the race, never split by more than a second, but the young Australian was never close enough to make a move.
The lead group included the top five or six cars for a time, but that eventually broke apart.
In the closing laps, the top four ran together before Tim Tramnitz and Sami Meguetounif began battling, allowing Mansell and Browning to break clear at the front.
The leading duo skipped over a second clear of those behind, crucially moving out of DRS range, with three laps remaining.
Browning was ultimately too strong and even marginally extended his lead in the final laps, crossing the line 1.2s clear at the chequered flag.
A fine second for Mansell equals his best result, and the third F3 podium of his career, with Tramnitz rounding out the top three.
The Formula 3 Championship heads next to Melbourne for Round 2 in support of the Formula 1 Australian Grand Prix on March 22-24.
