Piastri won the race of the season in Baku after withstanding incredible pressure from Ferrari’s Charles Leclerc.
The Australian took the lead on Lap 20, with Leclerc within DRS until the very last laps of the race.
Try as the Monegasque driver might, Piastri had his advances covered in a sensational display of defensive driving.
It followed an aggressive move to steal the lead, with the McLaren pilot sending it up the inside at Turn 1 from a long way back.
“When I watched it live and I saw him going, my instinct said, he’s going to go long,” Stella confessed.
“The delay in the braking point was like, if Leclerc braked there, that must be the braking point, and [Piastri’s] delaying.
“The precision in the execution to then actually be on the inside apex kerb in corner one…
“I was surprised, but Oscar is always surprising us with his talent, with his ability, and I would say today he gave also a demonstration of his mental strength.
“He drive like a driver than has a lot of experience, that has been under this kind of pressure before, that can look with won eye at the mirror, with the other eye where is the braking point.
“Oscar did it again with great level of precision and pretty controlled; even when he was talking on the radio seemed very, very much under control.
“Phenomenal driver, brilliant drive today.”
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Once ahead, Piastri was forced to defend on multiple occasions.
The Australian worked to build a buffer through the middle third of the lap to protect himself from DRS attack down the long front straight.
And while for the most part that worked well, there were instances when Leclerc was close enough to show his nose by the time they reached Turn 1.
On every one of those occasions, Piastri had the move covered, defending cleanly and hitting his marks to repeatedly thwart the Ferrari driver.
“I think it’s a combination,” Stella said when asked how his young driver was able to be so resilient.
“Ninety percent is Oscar, I think his judgement.
“The most difficult one will have been the first one. When you do the first one of these kind of manoeuvres, actually you don’t have references.
“After the first one, you will have found some references and therefore I think later on, it became easier for him.
“But when you do it the first time, you really have to judge things very precisely, not to be under attack braking for corner three with the next DRS zone for corner two.
“Where the 10 percent of the car comes to Oscar’s advantage is that the car has good traction,” he added.
“We know that our rear end is good, especially when we are around 100kph or more, which is where you are in corner one.
“This is definitely something that Oscar did exploit, but it wouldn’t work without his precision from a driving point of view.”
An important element in Piastri’s victory was the contribution of Lando Norris.
In the latter stages of the opening stint, Piastri had slowed after taking too much out of his tyres in the early stages in pursuit of Leclerc.
That left him vulnerable to Sergio Perez, who pitted a lap earlier than the McLaren driver and posed an undercut threat.
However, the Mexican found himself behind Norris on his out lap, who slowed just enough through the middle sector to delay him such that Piastri could pit and rejoin ahead.
“That message was because of Perez,” Stella said of the instruction given to Norris from the pit wall.
“Perez was undercutting. Effectively, without Lando’s help, Perez would have [rejoined] ahead of Oscar and the race could have unfolded in a completely different way.
“So I think 50 percent of Oscar’s victory today is shared with Lando.”
That contribution comes as McLaren revealed it would work to favour Norris where it could in his quest to win the drivers’ championship.
A poor qualifying however left him out of position and therefore down the order comparative to his team-mate and was therefore employed in the services of Piastri instead.
“We had a conversation before the weekend where we would bias one way or the other, but for us, we approach every weekend trying to maximise the result for the team,” Stella reasoned.
“If one driver needs help, we will do it, and the other driver will do it.
“That’s a point of strength for us when you compete within such a tight competition.”
Victory for Piastri leaves him fourth in the drivers’ championship, 91 points back from title leader Max Verstappen.
Norris, who was classified fourth, is now 59 points behind with seven races remaining, while McLaren now leads the constructors’ championship by 20 points.
It’s the first time since 2014 that the squad has headed that competition.