Valtteri Bottas relied on his usual Friday form to clock in fastest in the first practice session for this weekend's Spanish GP
But the Finn enjoyed just an 0.033s advantage over Red Bull's Max Verstappen, the Dutchman using a set of soft tyres at the very end of the session to secure his runner-up spot.
Behind the two leaders, Lewis Hamilton was third, 0.123s adrift from his teammate while McLaren's Lando Norris was once again the leading midfield contender.
Barcelona is familiar territory for F1's teams and drivers, and indeed most of the latter could likely circulate around the Circuit de Catalunya with their eyes closed, not that anyone would actually try doing it!
Practice kicked off on a warm 35.8°C tarmac and amid an ambient temperature of 22.2°C, but with a configuration change at Turn 10 which is no longer the semi-tight hairpin-like corner it used to be but a widened and faster left-hand curve.
The field also featured two permutations for FP1, with Alfa Romeo's Robert Kubica replacing Kimi Raikkonen and Roy Nissany taking over George Russell's Williams.
Half the grid, led by Red Bull's Sergio Perez, sprung into action at the outset, eager to kick off the now shorter 60-minute practice session, and eagerness got the better of Haas' Nikita Mazepin who enjoyed his first off-track excursion after just four minutes.
After several drivers traded places at the top of the timesheet in the opening 15 minutes, Hamilton – running on the rad tyre - set the first relevant benchmark at 1m19.675s, the Mercedes driver followed at that point by Alpine's Fernando Alonso, Verstappen, Bottas and Lando Norris.
But 30 minutes in, popping up out of nowhere on a set of soft tyres, Aston Martin's Sebastian Vettel shaved 0.411s off Hamilton's best. But the reigning world champion, now also on the soft compound, recouped the top spot in short order, lowering his best time to 1m18.808s.
Bottas followed suit but remained just a whisker behind in P2, followed by Norris, Gasly and Vettel. But the Finn pressed on to snatch P1, 0.123s aheadof Hamilton.
With 15 minutes left on the clock, Kubica triggered a red flag after losing the rear of his car mid-way through the new Turn 10 sequence and beaching the Alfa in the gravel.
The session resumed with 10 minutes to go, and with Verstappen bolting on a set of softs for the first time in the session. The Dutchman put the rubber to good use as he dispatched Hamilton for P2 behind Bottas.
The positions remained unchanged in the final minutes of running, with Mercedes and Bottas thus drawing first blood, but Red Bull and Verstappen just 0.033s adrift.
Behind Hamilton in third, Norris, Leclerc and Sainz capped off the top six, while Gasly, Vettel, Perez and Stroll rounded off the top ten.
Further down the field, both Alpine drivers, Esteban Ocon and Alonso, were beyond the first half while Daniel Ricciardo was a disappointing P14, some 0.7s slower than his McLaren teammate.
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