New McLaren recruit Daniel Ricciardo led the opening morning of Formula 1’s pre-season test in Bahrain as Mercedes became the first team to hit major trouble.

Ricciardo initially moved to the top of the timesheets during the second hour of the first day of running at the Bahrain International Circuit, before further lowering his benchmark to a 1m32.203s on C2 tyres in his Mercedes-powered McLaren MCL35M.

Reigning world champions Mercedes suffered an early setback in the opening session of the Bahrain test when it discovered a gearshift issue after Valtteri Bottas had completed just a single installation lap in the first hour.

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The problem forced Mercedes into a gearbox change that kept Bottas sidelined in the garage for nearly three hours before the Finn re-emerged for the final half an hour of the session.

It marked a far from ideal start for Mercedes given the limited testing time this year, with teams restricted to just three days of running - the equivalent of 1.5 days behind the wheel for each driver.

Bottas is set to hand over the W12 to seven-time world champion Lewis Hamilton, who will get his first chance to sample Mercedes’ latest F1 machinery during the afternoon session.

Pierre Gasly completed more laps than any other driver (74) as he ended the morning second-quickest in AlphaTauri’s AT02 with a time that was just 0.028s shy of Ricciardo’s session-leading time on the C3 compound.

The Frenchman headed Max Verstappen as Red Bull’s RB16B broke cover for its public track debut after the Milton Keynes squad had elected to withhold images of its updated car following its launch.

Verstappen was among a number of drivers who suffered off-track excursions with blustery conditions in Bahrain providing a challenge throughout the morning.

Esteban Ocon was the only other driver to get within a second of Ricciardo’s effort in his new-look Alpine, which raised eyebrows with its bulbous engine cover and airbox design.

Charles Leclerc was fifth-fastest for Ferrari and caused the first red-flag stoppage of testing in 2021 as he pulled over at Turn 4 with only 10 minutes remaining on the clock.

Alfa Romeo’s Kimi Raikkonen was next up in sixth ahead of former Ferrari teammate and new Aston Martin signing Sebastian Vettel, whose running was briefly curtailed when an issue caused him to stop at the end of the pit lane.

Williams test and development driver Roy Nissany was eighth as the Formula 2 racer conducts the first day of full running behind the wheel of the team’s new FW43B.

Ahead of his debut F1 season, Mick Schumacher could only manage 13 laps after losing valuable track time when Haas carried out a gearbox change after encountering a hydraulic problem.

Bottas ended the morning session at the bottom of the timesheets after completing just six laps - the fewest laps of all.

2021 F1 Bahrain pre-season Test Day 1 - Lap times at 2pm