He was the only Red Bull driver in action in Bahrain yesterday, completing 91 laps while other teams swapped out their drivers.
His team-mate, four-time champion Max Verstappen, took over last night for the third and final day of testing.
While the 23-year-old Kiwi got through a reasonable number of laps, he also spent a lot of time in the team garage, Red Bull saying the car needed regular servicing and setup tweaks.
Lawson’s RB21 also had water system issues that kept him in the garage for more than half an hour during the day’s first session.
"It’s been a very busy day.
"A few of our runs were cut short — obviously we had the weather [rain] to play in there as well, which honestly wasn’t great timing for us, every time we went out.
"But for me it’s just great to get a full day in the car, learning more about it, and obviously this is all extremely valuable going into Melbourne."
Red Bull technical director Pierre Wache said Lawson was responding well to the car, and vice versa.
"We had wanted to get a total insight into the car today, and understand its full direction, but it was also difficult to judge the performance of the car in these conditions and get a lot of the temperature on the tyres.
"But Liam responded well today, and his feedback was very close to Max’s.
"We have good understandings to take into the final day of testing now, with Max at the wheel."
Lawson was seventh fastest on the second day of testing, his best time of 1min 30.252sec more than 1sec slower than Williams driver Carlos Sainz.
Behind the new Williams driver were the two Ferraris of Lewis Hamilton and Charles Leclerc, followed by the Mercedes of George Russell and Andrea Kimi Antonelli.
Sainz completed the most laps of the second day, 127.
Like Lawson, Sainz was in the car for the entire day.
The last day of testing started last night, and the season begins in Melbourne on March 16.
— RNZ/APL
