McLaren's Lando Norris started on pole for Saturday morning's 19-lap sprint race but after going off at the start he fell down to seventh. That became sixth at the chequered flag due to Fernando Alonso's retirement, finishing in front of team-mate Oscar Piastri but behind both Ferraris.
Its race pace relative to the Scuderia seemed in line with the Woking team's muted expectations for the weekend, but that picture completely changed on Sunday when Norris split the Red Bulls to finish second, while Carlos Sainz and Charles Leclerc failed to finish in the top-five.
Norris said there was "nothing pointing" to the team's better-than-expected competitiveness on Sunday, but team boss Stella suggested the cooler conditions provided a possible explanation.
"In fairness, in the sprint, we didn't see that we had race pace that would have allowed us to finish ahead of Ferrari. It was in line somehow with what we expected before coming here," Stella said.
"So it's a bit of a surprise, especially in terms of race pace. We know that we are strong when we have new soft rubber, we can do a good job for a single lap, but when we put laps one after the other, we tend to lose some performance.
"But I think somehow the track conditions and the cold conditions, the fact that there was no sunshine, helped keep the rear tyres under control. And therefore we could use the strengths of the car, like we saw in qualifying.
"The rear axle especially was not overheating. While if we look at the sprint, I think we had a bit of overheating and Ferrari seemed to be more comfortable."
Piastri finished eighth after sustaining damage in the safety car collision between Daniel Ricciardo and Lance Stroll, with Ricciardo's RB tagging his diffuser that Stella says cost him up to fourth-tenths per lap.
"It was a big loss," Stella explained. "Oscar had damage on the diffuser, he lost a significant amount of rear downforce, equivalent to four-tenths of a second, something like that.
"When we heard the numbers, I wasn't very optimistic that we could have held positions like Oscar has been able to do.
"His result is less noticeable than Lando's, but I think he did a good job in trying to understand how to drive the car when he lost so much rear downforce. The car was very oversteery.
"He managed to make some adaptations and keep [Lewis] Hamilton behind, so that's also a strong result."
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