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Piastri qualified fifth fastest, one place back from team-mate Lando Norris, but ahead of both Ferraris and both Mercedes.
That performance came despite the Shanghai circuit not favouring the McLaren MCL38 and the squad having low expectations heading into the event.
On Friday, Norris qualified on pole for the F1 Sprint (in wet conditions), though fell to sixth in the 19-lap hit out after being forced wide at the opening corner by the fast-starting Lewis Hamilton.
Piastri was seventh, 2.7s further back, while race winner Max Verstappen was more than 20 seconds up the road as the pair struggled for pace in the race.
“I think fourth and fifth is a good result given there’s quite a few corners on this track – all of them – that we thought would be a bit of a struggle for us,,” Piastri said of McLaren’s qualifying performance on Saturday evening in China.
“To be especially ahead of the two Ferraris is a very good effort for us.
“We saw in the Sprint [on Saturday] that the race tomorrow could be a bit more difficult for us,” he added.
“I think qualifying is probably our our peak,” headed.
“We are maybe a little bit out of position in where we’ve qualified, in a good way, and we’ll see how long we can hang on in the race.”
A revised Sprint format this weekend has seen teams able to change their cars following Saturday’s encounter.
Last year, car set-up was locked from Friday afternoon but tweaks for this year see that lifted following the Sprint.
However, with no practice between the Sprint and qualifying, any refinements are a step into the unknown.
“Any possibility to reopen parc ferme after the Sprint I think has two implications,” said team boss Andrea Stella.
“The first one is that the weekend is slightly more forgiving because if you got some ride heights wrong or you see that the balance needs adjustment based on the tyre behaviour, for instance, you can do it.
“And this, I think, at the same time allows you to be slightly more aggressive in the first place in terms of what direction to take.
“We actually, from a purely engineering point of view, found this interesting.
“We found it interesting because we had the opportunity to see the balance in the Sprint and like in events like today where ethe tyres go off so much, you understand what you need to adjust or what you would ideally try to adjust in the car.
“So I think pretty much all teams will have made adjustments from a set-up point of view – we certainly did, and we hope that [in the race] will hep with our tyre degradation.”
The 56-lap Chinese Grand Prix begins at 17:00 AEST.
