Lance Stroll said he was left baffled by a "terrible" Turkish Grand Prix that saw him tumble from first to ninth when his Racing Point lost pace after leading for much of the rain-hit race.
The Canadian started from his maiden F1 pole position and made the most of a good start to stretch a sizeable lead during the first stint, in which he looked as though he would dominate the afternoon.
But as the track dried up, a switch to intermediate tyres caused graining issues that stopped him in his tracks and he went from a 10-second lead to end up one minute and 12 seconds behind eventual victor Lewis Hamilton.
"I don't know what happened," Stroll told Sky Sports F1. "I don't understand. We had so much graining on the first set of intermediates that we decided to pit because we were losing seconds a lap. I don't know where it came from, it happened instantly.
"We started the race on full wets, then we put an inter on and I was quite far up the road. [The next set] was new but it just grained again. Massive graining and no pace. We will have to look into it. It was pretty terrible."
Team-mate Sergio Perez managed to guide his car home to the runner-up spot, the team's second podium of the season, getting his intermediates to work better than Stroll's and staying out for the rest of the race.
That podium helped Racing Point retake third in the tight constructors' title battle, but Stroll failed to see the bright side.
When asked if it was a good day for the team, Stroll said: "For sure... [but] it is just frustrating when you are in the lead by 10 seconds and then all of a sudden you finish ninth.
"I don't understand how that happens. I mean, I do, it is graining but we just need to look into why it hit me so much harder than the other car. I am not so sure why."
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