With Bottas having opened proceedings on Monday before handing over to the Briton in the afternoon, Mercedes confirmed that Tuesday would see Hamilton run in the morning before handing over again.
However, instead, when the W09 rolled out of its garage it was the Finn at the wheel, and there he remained for the remainder of the day.
"With the weather conditions being up and down and the loss of track time we had yesterday (Monday), it made sense to keep Valtteri in the car this afternoon," said Hamilton.
"Having run in the morning, he was comfortable in the car already and we would have lost about an hour of running time with the driver switch.
"With no real understanding of whether good weather was coming or not, I took the decision to sacrifice that time in order for the team to gain better understanding of the car by going through the run plan."
Of course, it is well known that Hamilton is no fan of testing, especially when the weather compromises running.
Nonetheless, it was another good day for Mercedes, Bottas completing 94 laps - the second highest mileage of the day - and finishing just 0.303s off Vettel's pace... on harder tyres.