Mercedes' Lewis Hamilton bounced back from an early stoppage to set the pace on the opening day of Formula 1's in-season test in Bahrain on Tuesday.
With the start of running delayed by 10 minutes so officials could move shipping containers away from a dangerous place at the exit of the pitlane, Hamilton then stopped on track after just 15 minutes, causing a red flag.
The problem was discovered to be an electrical disconnection but, once the W08 had been returned to pitlane, it was rectified and Hamilton was get on with his programme.
Hamilton conducted a mixture of longer and short runs throughout the day, with Mercedes making no secret of the fact that it wants to use this week's test to better understand how to manage Pirelli's 2017 rubber.
The Briton set his best lap of 1m31.358 seconds on soft tyres in the final hour, meaning he ended up 0.626 seconds ahead of Ferrari test driver Antonio Giovinazzi.
With championship leader Sebastian Vettel concentrating on Pirelli's 2018 tyre test programme - which meant he was not allowed to run any development parts - Giovinazzi was tasked with Ferrari's main work for the day.
Vettel's efforts were compromised, however, by an engine problem in the afternoon that limited his running.
Pirelli subsequently got agreement from other teams to extend its own private test programme by nearly three hours until 9pm local time, so it did not lose any of its hoped-for track time.
Morning pacesetter Daniel Ricciardo, who worked on aerodynamic evaluation in the morning before tyre work in the afternoon, ended up third overall.
However, his day was cut short when he suffered a Renault engine failure in the afternoon and stopped at Turn 1.
A replacement power unit will be fitted overnight to allow Pierre Gasly to run on Wednesday.
"It just went," said Ricciardo.
"It's sleeping at the moment. I am not sure if that one is going to wake up."
Ricciardo was not the only driver to suffer a Renault problem, with GP2 racer Sean Gelael also hitting trouble in the morning when his Toro Rosso stopped with a suspected engine failure.
Gelael was able to get back out later in the day, though, causing another red flag later in the afternoon, before ending up eighth quickest.
Romain Grosjean was fourth fastest, his main focus was to evaluate new Carbone Industrie brakes, with Haas wanting to work out whether or not to make the switch from current supplier Brembo.
The Frenchman ended up ahead of Williams driver Felipe Massa and Renault's Nico Hulkenberg.
There were engine woes for Honda, too, with McLaren development driver Oliver Turvey only able to complete two installation laps in the morning.
Honda had discovered a water leak in the ERS, which prompted the need for a replacement power unit to be fitted.
Turvey was able to get running again in the final hour and completed 17 laps, although ended up at the bottom of the timesheets.
TUESDAY TESTING TIMES: