Piastri had demonstrated how difficult it is for the driver on pole to lead by the end of the first lap at Spa by losing the sprint race win to Red Bull’s Max Verstappen.
The Dutchman slipstreamed past Piastri up the hill to Les Combes, and then held the McLaren at bay for 15 laps, while Norris followed closely in third.
In the grand prix, it was Norris in front, with Piastri in second and Piastri had been thinking about the opportunity this presented him since losing out on pole the day before.
McLaren team boss Andrea Stella said: “This weekend, Oscar, if anything, the only inaccuracy was in qualifying, where his laps weren’t perfect.
“At the same time, we have to say that after the sprint qualifying, he said, ‘Yeah, I’m in pole position, but maybe this is not the right place to be in pole position.’
“And as a joke, after the qualifying yesterday, he said, ‘That was not my best lap in Q3, but perhaps this is the best place not to have the best lap in Q3.'”
Sure enough, Piastri took the lead on lap one of the grand prix, just as Verstappen had the day before.
“I had a good run out of Turn One,” he said, “and then tried to be as brave as I could through Eau Rouge and was able to stay pretty close. After that, the slipstream did the rest for me.
“When I watched the onboard back, it didn’t look quite as scary as it felt in the car. I knew that I had to be very committed to pull that off.”
But Norris could have done a better job. For a start, he failed to build himself a gap over the finish line by arguably going too early at the restart. Then he made a mistake at La Source, which allowed Piastri to be right on his tail approaching Eau Rouge.
“I didn’t have the best Turn One,” Norris said. “So it’s hard to know how much that played a part. At the same time, Oscar came past me pretty easily. So even if I had a better Turn One, his run and the slipstream probably still would have got me.”
Stella said: “It would have always been very difficult for Lando to keep the position starting first at the safety car restart. At the same time, I think Lando didn’t help himself by not having a great gap on the finish line.”