Polewinner Christian Rasmussen, who grabbed the top spot in the dying moments of qualifying, led the 17-car field to green in the 35-lap race, holding off Foster.
Behind them, Danial Frost’s wretched weekend continued after a driveline issue ruined his qualifying, as he spun following contact with James Roe at the first corner.
Rasmussen and Foster pulled clear out front, as Kyffin Simpson held third from Hunter McElrea and points leader Siegel.
The race started in dry conditions but rain sprinkles were reported from lap four. Foster pushed hard in the early stages and put leader Rasmussen under pressure. A full-course yellow interrupted the event when Christian Bogle spun into the gravel trap at the exit of the Keyhole.
It went green again on lap 10, with Foster keeping Rasmussen in sight once more.
Rasmussen lost a huge chunk of time with 10 laps to go as the rain fell harder, and Foster passed him with an outrageous lunge around his outside at Turn 4, just making the turn after a huge lock-up.
Foster pulled away, despite a flat-spotted right-front tire, as Siegel spun out of fifth at Turn 11, causing another caution period as he became bogged down on the damp grass.
Behind the leaders, the only position changes were Reece Gold passing Jacob Able for sixth (which became fifth after Siegel’s spin) with 11 laps remaining, while Rasmus Lindh got the better of Enaam Ahmed for ninth after a fierce tussle.
The race went green again with four laps to go, with Foster leading Rasmussen, while Siegel restarted down in 15th. Simpson barged past Rasmussen at the Keyhole to take second, but had nothing for Foster, who won by 0.7s.
Rasmussen held off McElrea for third, ahead of Gold, Abel, Lindh, Ahmed, Josh Pierson and Jamie Chadwick.
