Antonio Giovinazzi went fastest for Ferrari on the opening day of Formula 1's in-season test at the Hungaroring.
The Ferrari junior driver banked 96 laps, setting a time under Sebastian Vettel's race lap record in the process.
His time, a 1:15.648s, came on a set of Hypersoft tyres, and proved 2.5s faster than Marcus Ericsson who was next best for Sauber.
Following last weekend's Hungarian Grand Prix, nine of the ten F1 teams remained for the test, with Haas electing to sit the two-day event out.
Toro Rosso fielded two cars, one for Brendon Hartley who ended the day third quickest, and a second for Sean Gelael who focused on 2019 tyre testing for Pirelli.
Gelael crashed in the afternoon, drawing a red flag shortly before rain interrupted running.
While most drivers banked close to 100 laps, Mercedes test driver George Russell completed just 49.
Russell's running was interrupted by a gearbox problem in the morning, costing the team track time before the rain arrived later in the day.
At Williams, Oliver Rowland's program totaled just 35 laps as the team tested a prototype 2019-spec front wing.
“We had spent a long time preparing for this event, concentrating on 2019 aero regulations,” explained Rob Smedley, the team's Head of Performance Engineering.
“The team did a good job to prepare for it and everything went more-or-less according to plan, and we collected all the data we needed.
“We brought a 2019 aero specification front end, and all of the data that we were able to collect will really enrich the 2019 program going forward.”
Force India also tested a 2019 front wing concept, which is both wider and simpler than the solutions used this season.
Nicholas Latifi compelted 103 laps of running for the team, ending the day seventh of the ten runners.
“It was overall a successful day,” said Tom McCullogh, the team's Cheif Race Engineer.
“We managed to get all the aero data we set out to obtain, something that was critical for our 2019 car development.
“We had a new front wing on the car, alongside other test items and instrumentation.
“The heavy rain showers in the afternoon meant we had to cut our programme short, but we still managed a solid 103 laps so we can be satisfied with our work.”
Daniel Ricciardo ended the day sixth fastest for Red Bull, which was one of only four teams to use its race driver for the day.
Ricciardo set a best of 1:19.854s, the team focusing on long runs and testing elements with a view towards the 2019 car design.
The only other race driver on duty was Nico Hulkenberg, who completed 63 laps for Renault after an electrical issue kept him in the garage for much of the afternoon.
The two-day test concludes on Wednesday before teams head back to their respective factories to begin the summer break.
Result: Hungarian Formula 1 testing, Day One
|Toro Rosso Honda
|Red Bull Renault
|Force India Mercedes
|Toro Rosso Honda