Valtteri Bottas was left ruing his qualifying strategy after Lewis Hamilton pipped him to pole position for the Portuguese Grand Prix.
Both Mercedes drivers switched to medium tyres for the final runs in Q3 on Saturday but Hamilton left the garage first, giving himself time for two flying laps.
Bottas opted to only go for one shot and initially took provisional pole from Hamilton, who pipped him on his second run.
"We decided to go for medium because of the previous feeling in qualifying, it felt a tiny bit quicker than the softs," Bottas, who was quickest in all three practice sessions, explained.
"Then it was choosing if we do two timed laps or one timed lap. I went for that, it was my decision because it worked in Q2. But apparently it seems like doing two timed laps like Lewis was better.
"It was a decent lap, not perfect. It's been tricky here to get really clean laps this weekend because of the way the track is. The lap was good. Ultimately I should have gone for two timed [laps] as well."
Hamilton will start from the front of the grid for the ninth time this season and the 97th time in his career, giving himself a great chance of securing a record-breaking 92nd win in Portimao.
"It's amazing. I can't tell you how hard that was today. Yes, we've got a great car but you have to drive the nuts off of it to pull out a lap," said Hamilton.
"Valtteri's been so quick this weekend, he's topped every session. So I've just been digging and digging and digging to find that extra time.
"At the end, I chose to do three laps to give me a chance at beating his time and I think [Bottas] decided to do one, so I was like, 'Okay, this could provide me with an opportunity.' And it worked. That last lap, it got better and better as I went through it.
"The team communicate really well and gave both of us the option to either go on to the soft or the medium, we both chose to go medium, he chose one lap, I chose to do three. I got out there nice and early."
Red Bull driver Max Verstappen will start from third on the soft compound, while both Mercedes drivers will be on mediums.
"The tarmac is quite difficult to bring the tyres in, so it's a bit hit and miss. I'm happy though," said Verstappen.
"I think the lap in Q3 was pretty decent, it's very difficult to get the front tyres and the rear tyres to match but again, P3 is not too far behind and of course a lot to play for tomorrow and hopefully we can stay close.
"Turn one is not really a place to dive. I think the start will be important but even then, we don't really have enough information about how the tyres are going to hold up, so we'll just feel our way into the race and see what's going to happen."