Lewis Hamilton has topped the opening day of the Bahrain in-season test for Mercedes despite focusing on long runs and race pace as it aims to strike back against Ferrari.
Hamilton's test got off to a poor start having stopped on his opening installation lap at turn 10 but after a quick 30-minute fix he enjoyed largely trouble-free running to complete a full programme for Mercedes with 97 laps.
His best effort of 1m 31.358s set in the afternoon was enough to give him the fastest time of the day despite not targeting outright times as Mercedes looked to make race pace improvements after losing out to Ferrari's Sebastian Vettel in last weekend's Bahrain Grand Prix.
Antonio Giovinazzi stepped in for Ferrari testing duty after his two F1 races for Sauber in Australia and China and was able to put the SF70H second on the timesheet with a best effort of 1m 31.984s having produced 93 laps on his official debut for the Italian manufacturer.
At the other end of the times it was another frustrating day for McLaren-Honda as development driver Oliver Turvey could only notch up 16 laps after suffering a water leak on his ERS system which forced an entire power unit change.
The switch cost the Woking-based team over eight hours of valuable track time and with the British driver failing to post a competitive lap time which left him bottom of the timesheet.
Morning's fastest driver Daniel Ricciardo ended his day third overall for Red Bull despite suffering an on track stoppage at turn one midway through the afternoon. The Australian driver was still able to notch up 45 laps with a best effort of 1m 32.349s.
Romain Grosjean enjoyed a trouble-free test day in the Haas experimenting with different after the ongoing troubles have continued to resurface in 2017. The French driver produced 86 laps with a fastest time of 1m 32.452s.
Further back Felipe Massa ended the day fifth on the times after completing only the afternoon session in the FW40 after team-mate Lance Stroll took on driving duties in the morning as scheduled.
Off the back of his maiden points finish for Renault, Nico Hulkenberg notched up 73 laps with a best time of 1m 33.624s to split the Williams drivers in a day of relative problem-free running.
Toro Rosso gave an F1 debut to Indonesian F2 driver Sean Gelael in Bahrain as he completed a strong 78 laps, to head up Force India's development driver Alfonso Celis Jr and Sauber's Marcus Ericsson who completed the most laps of any driver with 106 in the C36.
With teams not focusing on outright pace while conditions were hotter and windier than in the Bahrain Grand Prix, lap times were unlikely to challenge the pole position lap time set by Valtteri Bottas on Saturday of 1m 28.769s.
Bahrain GP race winner Sebastian Vettel was also on track in his Ferrari but as an exclusive Pirelli tyre tester and after missing around four hours of track time with a technical issue he was given special dispensation to continue the test into the evening with an expect finishing time of 9PM local time (7PM BST).
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