The Australian battled a brake-by-wire issue for much of the race which curtailed his pace and saw the team close to retiring the car.
Piastri made a lightning start, rising to 13th on the opening lap before an early stop.
His race then unravelled with the braking issue but still reached the chequered flag, albeit in 19th.
“He needed to drive the entire race with a problem on the brake-by-wire, which Oscar was excellent in being able to cope with,” Stella confirmed to media, including Speedcafe.
“After having locked the tyres for three, four times, he kind of realised how he needed to adapt the way he was braking to the issue.”
In the early laps, Stella admitted McLaren considered hauling Piastri out of the Miami GP.
“There were two critical factors which led us to think we should retire the car,” he explained.
“The first one is that the rear brakes started to overheat, and the second one is that Oscar went long in a couple of corners because he was pretty much using only the front brakes as we were trying to resolve the problem.
“For both things, we kind of found some settings and also adaptation of the driver, which meant that we could keep the brake temperature under control and also we could have a relatively good level of consistency in braking.
“So we decided to stay in the race. We know that there weren't many opportunities but we are here to race, we stay in the race.”
It was a difficult race for McLaren with Lando Norris finishing only two places better than Piastri after sustaining floor damage at the first corner.
“After a decent weekend in Baku from a performance point of view, we had a reality check,” Stella admitted.
“I think the information we gained here help[s] us understand that some development directions still need to be pursued, like improving the car off brakes, off throttle – at the moment the car just doesn't work in this condition.
“At tracks like this, this becomes too much of a limitation.
“So we take away some important learnings for development.”