SAKHIR, Bahrain -- Red Bull's Daniel Ricciardo set the pace on the first morning of in-season testing at the Bahrain International Circuit.

Tuesday is one of four open in-season test days planned for this year ahead of a second day in Bahrain on Wednesday and two further days testing after the Hungarian Grand Prix in July. With temperatures over 32C, the conditions were harsh for cars, tyres and drivers, but the opportunity to test new parts outside a race weekend saw all teams hit the track.

The green light at the start of the session was delayed ten minutes while leftover freight from the grand prix weekend was moved from the pit lane entrance, but when testing got started the teams wasted no time heading back out on track. It didn't take long for the first stoppage however, with Lewis Hamilton's Mercedes coming to a halt with an electrical disconnection after just 14 minutes of running.

It took 25 minutes for the car to return to the pits on the back of a flatbed truck, in which time a small congregation of photographers and rival team engineers had gathered around the garage for its return. Unfortunately for them, the car -- and its floor -- were covered when it was unloaded from the truck behind some Mercedes-branded screens. Business continued as usual several minutes later.

Twenty minutes later and another red flag suspended the session, this time for the Toro Rosso of F2 driver Sean Gelael, which had stopped ahead of Turn 11 with whisps of smoke coming from its airbox. Soon after running resumed the Mercedes got back on track and the Toro Rosso also returned before the midway point of the day.

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But the problems for both Mercedes and Toro Rosso were minor compared to the issues at McLaren-Honda. New power unit parts had been flown out especially for this test but the car completed just two laps in the morning before a water leak on the Energy Recovery System forced the to stop. After a series of MGU-H failures over the Bahrain Grand Prix weekend, this week's test was seen as an opportunity to kick start the recovery process but Tuesday morning's issues have resulted in a slow start. Test driver Oliver Turvey was at the wheel of the car to correlate on track running with his simulator work, but is due to hand over the car to race driver Stoffel Vandoorne on Wednesday.

At the top of the timesheets, Hamilton's 1:32.822 sat as the fastest time for the majority of the morning before Daniel Ricciardo logged a 1:32.349 just before the day's midway point. Ricciardo's best lap had the fastest first sector by some way, a strong middle sector but the third and final sector was 0.3s off Hamilton's best. Nico Hulkenberg in the Renault and Lance Stroll in the Williams were both within a second of Hamilton's best time, with Stroll due to hand the Williams over to Felipe Massa in the afternoon.

Ferrari was the only team to run two cars during the day as Sebastian Vettel kicked off Pirelli's 2018 tyre testing programme in a second SF70H. Reserve driver, and Sauber substitute at the first two races of this season, Antonio Giovinazzi was behind the wheel of the other car, which was working purely on a Ferrari-focused testing schedule.

Times at 13:30

1. Daniel Ricciardo, Red Bull, 1:32.349, 43 laps

2. Lewis Hamilton, Mercedes, 1:32.822, 27 laps

3. Nico Hulkenberg, Renault, 1:33.624, 43 laps

4. Lance Stroll, Williams, 1:33.729, 35 laps

5. Romain Grosjean, Haas, 1: 33.838, 40 laps

6. Antonio Giovinazzi, Ferrari, 1:34.967, 62 laps

7. Sebastian Vettel, Ferrari, 1:35.043, 48 laps

8. Marcus Ericsson, Sauber, 1:35.317, 52 laps

9. Alfonso Celis, Force India, 1:37.661, 21 laps

10. Sean Gelael, Toro Rosso, 1:38.111, 27 laps

11. Oliver Turvey, McLaren, No time, 2 laps