Norris had been running third in the lead train of cars during the second stint of the Marina Bay race, as polesitter Carlos Sainz controlled the pace at the front to bunch the field up.
But Norris found himself promoted to second when George Russell ahead of him, and Lewis Hamilton behind him, were switched to medium tyres under a virtual safety car on lap 44.
With the medium compound proving to be the optimum tyre, and both Mercedes suddenly lapping more than one second faster than Sainz and Norris, it quickly appeared as though the German manufacturer would charge through to take a spectacular win.
Stella, sitting on the pitwall at the time, believed Norris' podium shot was gone when he saw Mercedes peeling off into the pits for their fresh mediums.
"When I saw them going onto sets of brand new mediums, I thought they're going to pass us," explained Stella.
"The new medium was the correct tyre for that situation, considering the stint length.
"We considered actually pitting, but we would be on a used soft [as Norris had no other tyres available] and we were nervous of 16-17 laps flat out on a used soft. So we decided to stay out. We would have pitted in case of a safety car, but not in case of the virtual safety car."
Stella was so resigned to losing out to the Mercedes that he started urging himself not to be too distraught when it happened.
"It was tense, but I was not very optimistic," he explained. "I was just waiting for it to happen and be ready to say: 'Don't get too disappointed.' They had double medium, it really played well into their hands with this virtual safety car, and we tried our best. But then things changed."
Stella suspected that Russell's charge was halted by potential brakes or tyres overheating as he followed the two lead cars, which prevented him from being able to launch an assault before the last lap crash that put him off.
"I think soon they lost a little bit of this momentum, and getting traction with the softer tyres," added Stella. "Then the last three laps, I said: 'Maybe we can do it.'
"But I don't think we would have done it without the collaboration with Carlos. Let's call it like this, because Carlos, in his own interest, he wanted to have Lando within the DRS.
"So the time when Lando lost it in trying to defend, I think Carlos actively kind of waited for Lando to get within DRS. So it was a bit of teamwork between two previous team-mates for a great result for both teams."
