Russian teenager Sergey Sirotkin needed bigger shoes as he stepped up for a Formula One test with Sauber in Bahrain on Tuesday that gave him enough mileage to qualify for a super license.
The 18-year-old reserve, being prepared by Sauber for a possible Formula One future, did 300km and 76 laps - more than a race distance - of the Sakhir circuit that hosted the country's grand prix on Sunday.
He took it in his stride, posting the eighth fastest time of the 11 drivers present - and best of those who do not have a race seat - with a time of one minute 39.023 seconds, but he also felt the pinch.
"On my fast lap in the morning I made a few mistakes, so I probably lost a second," said Sirotkin in a team statement.
"In the afternoon we had some difficulties with my shoes. They were too small, so it was pretty painful when I was braking. When we changed the shoes, it was still not the best and difficult to drive."
Sauber's test engineer Paul Russell said the driver had done well in a car he had never driven before on an unfamiliar layout.
"He handled it pretty well. The lap times were very good. He seemed to be learning the car and the track quite well," said Russell.
Sirotkin's compatriot Daniil Kvyat, the 19-year-old who races for Toro Rosso, was slowest on the timesheets in 1:40.452 with Sunday's runner-up Nico Rosberg quickest for dominant Mercedes in 1:35.697 and completing 121 laps.
Germany's Nico Hulkenberg was second fastest for Force India with Ferrari's Fernando Alonso third and Denmark's Kevin Magnussen fourth in a McLaren.
McLaren had originally planned for Britain's Oliver Turvey and Belgian Stoffel Vandoorne to test on Tuesday and Wednesday but decided after Sunday's race to keep Magnussen in the car in the interest of continuity.
Both the Dane and team mate Jenson Button failed to finish Sunday's race.
Lotus, who have yet to score a point in three races and did little testing pre-season, suffered more problems with the Renault power unit and Venezuelan Pastor Maldonado managed only 16 laps.
(Reporting by Alan Baldwin in London, editing by Pritha Sarkar)