The 24-year-old did everything right at the Lusail circuit, winning the Saturday sprint from pole position and leading Sunday's race from pole until a team strategy blunder left him having to settle for second to Red Bull's Max Verstappen.
The Australian said he was speechless with what had happened and McLaren were quick to apologise for a mistake that left him third overall and 16 points behind teammate Lando Norris, who finished fourth. Verstappen is second, 12 off the lead.
"Clearly Oscar was in control of the race and deserved to win it, and we lost the podium as well with Lando," Stella told reporters.
"Oscar, from a points point of view, is definitely in condition to win the title," added the Italian.
"We have seen before in the history of Formula 1 that when you have this kind of situation sometimes it's the third one that actually wins."
Lessons from 2007 and 2010
Stella, who joined McLaren after years at Ferrari, spoke from personal experience.
In 2007 Ferrari's Kimi Raikkonen won the championship after going into the final race third overall and behind McLaren's Fernando Alonso and a rookie Lewis Hamilton, who ended up level on points and missing out by one.
In 2010 Sebastian Vettel took the first of his four championships with Red Bull after going to Abu Dhabi in third place and behind teammate Mark Webber, now Piastri's manager, and Alonso who was by then at Ferrari.
McLaren have said they are well aware of the precedents but will not abandon the policy of treating their drivers as equals and Stella emphasised that Piastri will be free to race while he still has a chance of the title.
"We will let the drivers be in condition to race each other but above all what's important for us is that we are in condition to beat Verstappen with one of our two drivers," he added.
"We want to be fair to our drivers, we want to race with integrity and we want to race in a way that doesn't surprise our drivers.
"So between now and Abu Dhabi there will be further conversations with Lando and Oscar. We will confirm our racing approach but certainly what I can say is that if any of the drivers is in condition to pursue the quest to win the title, then we will respect this."
