Daniil Kvyat hailed his "best race of the season" in P10 and debutant Brendon Hartley finished P14 in Austin – but one driver is set to be dropped for Mexico.
With Carlos Sainz moving on to Renault and Pierre Gasly having a wasted trip to Japan for the cancelled Super Formula finale, Kvyat returned to action in the US and Hartley was handed his debut by the Red Bull junior team.
However, Gasly is due to return for the next race in Mexico City, leaving Kvyat and Hartley uncertain about their futures.
"It was a great race. It was more than perfect, I must say,” Kvyat said.
“My best race of the season for sure. Fantastic. Got the maximum out of our car, very happy about the result.”
Kvyat was then asked whether he would stay, he said: "I don't know. I've done a perfect Friday, a perfect Saturday and an even more perfect Sunday, so I don't know what else I can do."
Hartley, though, seems resigned to the fact that he may be the one to lose out.
"I would like to [stay] but I guess I have to see now. I don't really know," he said.
"I think it's clear I would love to be here. Up to now I haven't been asking the questions, I haven't been pushing anyone on that.
"Even when I first had the call to come and have a test on the simulator, I didn't ask anything, I just did the job.
"I've tried to do the same this weekend. Let's see. I know there's another race coming up pretty quick, but I'm not holding my breath."