It proved to be a frustrating day for Valtteri Bottas at the Autódromo Internacional do Algarve in Portimão after a software glitch prevented him from finishing ahead of Red Bull rival Max Verstappen.
Bottas had won pole position for the Portuguese Grand Prix and held the lead at the initial start and then during a subsequent safety car restart that saw Verstappen take second from the Mercedes driver's team mate Lewis Hamilton.
But while Hamilton was able to pull off passes on both Verstappen and Bottas to take the lead on lap 20, Bottas went on to lose second to Verstappen when he slid wide on cold tyres following his pit stop.
"It was tricky today," he told the media in parc ferme immediately after the end of Sunday's race. "I don't know what happened in the first stint.
"Overall we had a strong package, I don't know why it didn't work in the first stint," he added. "I didn't have the pace for some unknown reason and we have to take a look at that. But I think the second stint was pretty good."
Even so, Bottas hopes of retaking the position in the remaining laps were thwarted by a problem with the exhaust temperature sensor. "We had a bit of an issue with a sensor so I couldn't get Max," he confirmed.
Mercedes team principal Toto Wolff gave further details of the issue to Sky Sports Italia. "Based on our speed on the straights he might even have managed to pass [Verstappen].
"The problem was we had a little gremlin in some engine software that we wanted to eradicate, and that did just the opposite," he explained. "That is something that we have to fix in our software."
Bottas did prove the pace of the Mercedes package by going on to pick up the bonus point for fastest lap in the race, after making a late pit stop to change on to a new set of the faster soft option compound.
"We had a good top speed on the straights today," Wolff confirmed. "The set-up we chose was the right one. A little to the detriment of downforce and drag, but quick on the straight. That worked well, ”
But Wolff said it was too soon to say whether Mercedes or Red Bull would prove to be the fastest car of 2021.
“The car was strong yesterday, which is a positive development but it's hard to say today," he commented. "I think both teams are on an equal footing, and you have to take P1 and P3 with the fastest lap."