The Swedes were dribbled away in the strategy race at Barber Motorsport Park.
Marcus Ericsson, who qualified as twelfth after skidding off the track in Q2, was never near the top in the race over 90 laps on the 3.8 kilometer long track.
Marcus did not get a good first pit stop and had neither strategy nor car to be able to reach the top-10 in the final stage of the race.
The ambition to challenge for the championship title has clearly taken a hit.
After the heavy crash in the wall in Long Beach, which probably cost a podium place, there was another placement down in the summary to ninth.
- We had no flow with our three-stop strategy.
I got too caught up in the "traffic" and it did not help that I was fast when I was allowed to drive freely, says Marcus to indycar.com.
Cheeky maneuver
Rosenqvist looked to be driving towards his best position for the season.
But the Arrow McLaren driver ended up completely wrong with the strategy and was forced to save fuel and lost from sixth to a modest 16th place in the finish.
For teammate Pato O'Ward, it was a success.
The Mexican made a cheeky maneuver on the 64th lap, where he passed the Dutchman Rinus Veekay up to a lead he kept into goal.
- I was tired of bad placements and wanted to show something else today.
"I am very happy for the victory," O'Ward told Viaplay.
Veekay was also beaten by last year's championship winner Alex Palou, Spain, who tops the summary.
Lundqvist saved the Swedish honor
Linus Lundqvist became this weekend's racing Swede in the USA when he took over the lead in the Indy Lights table after the season's first victory.
Linus had a tough battle with teammate in HMD Motorsports, the Dane Benjamin Pedersen, but kept away from pole position to victory.
- It was tight.
One of the most beautiful victories in my career, says Linus in a press release.
The next stop for Indycar and Indy Lights is the Indianapolis roadcourse (old Formula 1 loop) at the classic Indianapolis Motor Speedway facility May 13-14.