Foster remained calm throughout 4 restarts and was relatively unchallenged for all 45 laps of the two.645-mile, nine-turn temporary street track in the guts of the Motor City.
It was the second victory in a row for the Briton, whose closest rival was Caio Collett from HMD Motorsports.
“At first I just controlled the lead.” Foster said. “And then halfway through the gap I took quite a giant break with him (Collet), pondering he had killed his tires.
“But to be honest, he got here back quite strongly within the late stages of the race. It was close, but I feel we had enough attacks to stop him.
“And then unfortunately it ended in yellow, which is something we don't like to see. But I'm happy with the result.”
Collett finished second for the second 12 months in a row, ahead of teammate Callum Hedge.
Myles Rowe undoubtedly delivered the drive of the day after storming from nineteenth on the grid to complete fourth within the #99 HMD Motorsports entry into Force Indy. Jacob Abel, who began second, finished fifth.
When the competition ended with the primary laps to go before the green flag, championship contender Nolan Siegel was unable to start out from seventh place attributable to a broken driveshaft. He managed to return to his No. 39 HMD Motorsports entry after repairs, but was 4 laps behind.
Foster managed to get off to an excellent start when the green flag flew, clearly dividing the sector early on. Meanwhile, Collet moved into second on lap three after passing Abel entering Turn 3.
However, a caution got here on the next lap after Andretti Global rookie Bryce Aron lost form on the within line in Turn 7 and momentum led him to hit the surface wall hard.
Extended clean-up time allowed the race to be restarted on lap 9, and Foster once more made a smooth exit to achieve a 0.9s lead on lap 17.
Abel's third place was in danger on lap 20 after Michael d'Orlando, fighting for a probability to proceed racing next weekend, tried to overtake him in Turn 9.
However, this move didn’t repay because the two went side by side, with d'Orlando losing form on the surface, along with his left rear flippantly hitting the surface wall before spinning and sustaining minor damage. He was in a position to proceed but dropped to seventeenth, with Abel retaining third place.
The competition heated up again after 25 laps when the yellow flag was shown and Jack William Miller was temporarily stuck off target in turn one. On the restart two laps later, Foster continued his clean breakaway theme, but Abel was still at risk of the ultimate podium spot.
Andretti Global's Jamie Chadwick was putting the pressure on coming out of Turn 3 and into Turn 4 when she pulled back barely after which suffered a right rear puncture after being hit by Yuven Sundaramoorthy's front wing. This resulted in Chadwick and Sundaramoorthy being dropped from the starting list and out of contention for the highest ten.
Abel eventually dropped to fifth after passes from Callum Hedge and Rowe, who had began nineteenth.
Front wing damage struck Sundaramoorthy when his Able Motorsports machine was shown a yellow card after cornering in Turn 7 on lap 39.
The race restarted with five laps remaining when Foster was forced to once more defend his top spot heading into Turn 3 and hold that position as Collet was unable to make a move.
Caution returned with three laps to go after a multi-car crash in Turn 6, which began after Andretti Global's James Roe spun and took out Nolan Allaer (HMD Motorsports) and Niels Koolen (HMD Motorsports).
Despite passing to 3rd, Rowe was forced to offer up the position when the sector was returned to starting order before being cautioned.
The race finished under caution, with Foster escorting the sector to the checkered flag.
