Lewis Hamilton finished only 10th in second practice for the Azerbaijan Grand Prix as Fernando Alonso succumbed to further engine woes.
Hamilton, who trails title leader Sebastian Vettel by 12 points ahead of the eighth round of the championship here in Azerbaijan's capital city of Baku, was fifth in the opening session.
And the Briton could manage only 10th later in the day as Red Bull's Max Verstappen topped the order while Vettel finished fifth.
Hamilton's time - he finished 1.1 seconds adrift of Verstappen and one second slower than his Mercedes team-mate Valtteri Bottas - is slightly skewed because the triple world champion did not post a lap on the super-soft tyre, the quickest of the three Pirelli compounds available this weekend, after Jolyon Palmer crashed into the wall at turn eight.
Palmer's incident, midway through the 90-minute session, resulted in the action being temporarily suspended as they removed the under-fire Briton's mangled Renault and the ensuing debris.
It was another day to forget for Palmer, with the 26-year-old facing mounting speculation that he could soon be replaced, and so too for Alonso after his Honda engine conked out with 30 minutes remaining.
Alonso, who is already due to start Sunday's race from the back of the grid following a series of engine penalties, launched his headrest out of his McLaren as he ground to a halt.
"Engine, engine," the frustrated Spaniard said. McLaren are the only team yet to score a point this season and their relationship with Honda is now at an all-time low.
Palmer's crash and Alonso's demise were one of several talking points of a chaotic session at this street circuit which runs against the picturesque backdrop of the old city's walls.
While Palmer thudded the barrier at turn eight, he was not the only driver to struggle with the narrowest piece of asphalt on the Formula One calendar.
The twisty section which measures just 7.8 metres wide saw Vettel take to the escape road on a number of occasions after missing his breaking point, and in fear of a costly collision with the barriers.
And, although Verstappen set the fastest times in both sessions on Friday, the Dutchman ended the afternoon in the wall at turn one on an otherwise impressive day for his Red Bull team. With just minutes of the session remaining, the 19-year-old lost control of his car under braking and span into the nearside barrier.
Elsewhere, Daniel Ricciardo was third in the sister Red Bull, with Ferrari's Kimi Raikkonen fourth. Sergio Perez, who crashed out of the opening session, was seventh fastest for Force India.
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