Lewis Hamilton recovered from an early track breakdown to post the fastest time on the opening day of the two-day Test in Bahrain.

Hamilton's running hit an early glitch when his car required a lift back to the pits within the opening hour of the morning session.

The cause of the breakdown isn't known but only resulted in a 30-minute delay for the three-time world champion. Hamilton then posted a 1:31.358 in the afternoon to top the timesheets.

But there were yet more ongoing problems for McLaren-Honda who only managed a timed lap in the final 20 minutes of the day and were slowest, four seconds off Hamilton's time

The team reported they "detected a water leak from the ERS" on the MCL32's morning installation laps and elected to change the power unit as a result.

Antonio Giovinazzi, who drove for Sauber in the Australian and Chinese GPs, was testing for Ferrari and was second fastest, six tenths down on Hamilton.

Championship leader Sebastian Vettel was also in action but tested Pirelli's 2018 tyres on Tuesday and will revert to normal testing on Wednesday.

Daniel Ricciardo's Red Bull had set the pace during the morning session but ran into difficulties during the afternoon and had to be returned to the pits on the back of the recovery track.

Underling the importance Mercedes, beaten to victory at the desert circuit in Sunday's grand prix, are attaching to the event, both Hamilton, who rarely runs during in-season testing, and team-mate Bottas are participating this week.

Mercedes are focused on improving their long-run form during the test, with the W08 seemingly harder on its rubber than title rivals Ferrari during the opening three races of 2017.

Bahrain Test Day One Timesheet Driver Team Laps Fastest Time 1) Lewis Hamilton Mercedes 97 1:31.358 2) Antonio Giovinazzi Ferrari 93 1:31.984 3) Daniel Ricciardo Red Bull 45 1:32.349 4) Romain Grosjean Haas 87 1:32.452 5) Felipe Massa Williams 56 1:32.509 6) Nico Hulkenberg Renault 74 1:33.624 7) Lance Stroll Williams 35 1:33.729 8) Sean Gelael Toro Rosso 78 1:33.885 9) Sebastian Vettel Ferrari - Tyre Testing 89 1:33.894 10) Alfonso Celis Force India 71 1:33.939 11) Marcus Ericsson Sauber 106 1:34.550 12) Oliver Turvey McLaren 17 1:35.011

"We have some work to do in the test, trying to strengthen the car, strengthen our knowledge of the tyres to be in a better position for the next race," said Hamilton on Sunday night.

"The car is obviously good, but it's how we use our tyres in the races, particularly when it's warmer, although today it was quite cool. That is definitely the big question mark for us."

Oliver Turvey, behind the wheel of the McLaren-Honda after they rejected the opportunity to familiarise Jenson Button with their 2017 car ahead of his return at next month's Monaco GP, was limited to just 17 laps.

Honda have indicated they will be testing 'new ideas' this week but a full upgrade of their troublesome engine is not expected for another month.

Vettel was tyre testing for Pirelli on Tuesday

Romain Grosjean's Haas posted the fourth quickest time of the day ahead of Williams' Felipe Massa, who drove the afternoon session after Lance Stroll was in the car during the morning.

Renault confirmed they are using the test to introduce the 'first major upgrades of a season that will see a lot of progress and improvement' and Nico Hulkenberg was sixth.

Indonesian F2 driver Sean Gelael debuted for Toro Rosso and, after an an early setback when his car crawled to a halt, was eighth fastest.

Alfonso Celis was 10th in the Force India while Marcus Ericsson completed the most laps - 106 - in the Sauber but finished second slowest.

Bahrain Test Line-Up Team Tuesday Driver Wednesday Driver Mercedes Lewis Hamilton Valtteri Bottas Ferrari (tyre testing) Sebastian Vettel Ferrari Antonio Giovinazzi Sebastian Vettel Red Bull Daniel Ricciardo Pierre Gasly Renault Nico Hulkenberg Sergey Sirotkin Force India Alfonso Celis Sergio Perez Toro Rosso Sean Gelael Daniil Kvyat Haas Romain Grosjean Kevin Magnussen McLaren Oliver Turvey Stoffel Vandoorne Sauber Marcus Ericsson Pascal Wehrlein Williams Lance Stroll/Felipe Massa Gary Paffett

Don't miss the F1 Report: Bahrain GP Review on Sky Sports F1 at 8.30pm on Wednesday for the final word on the weekend's action.