If there is one weakness in Fabio Quartararo's MotoGP title armour it's Yamaha's poor wet weather form.

That was again illustrated during opening practice in Texas, when the Frenchman was the top M1 rider in just 15th place on the timesheets, 2.3s behind Marc Marquez (Honda) and 0.8s from title rival Francesco Bagnaia (Ducati).

But Quartararo insisted a 'big step' had been made compared to his previous wet weather outing, in practice at Misano.

"This morning it was pretty good," said Quartararo, who starts the COTA weekend with a 48-point lead over Bagnaia. "We made a big change to the setting compared to the last time we rode on the wet and I really liked it.

"Then we tried the medium rear and my feeling was much better, we made a big step.

"I think we still have a margin for improvement. We’ll use the next sessions to be in the top 10, but in particular I feel very happy about the change we made."

Team-mate Franco Morbidelli began his second weekend as a factory Yamaha rider in 17th place (+2.7s).

"The practice was decent. We are trying to understand and find a good basis also on the wet," said the Italian. "We are making some laps and try-outs on the setting to understand better what we need from the bike.

"We did that and moreover I needed to understand how the leg was working and it’s good because I don’t feel pain anymore, I am just missing some strength, so this is good.

"At least this morning on the wet I did not feel any pain and that’s good. Now we keep on working and let’s see what happens."

The Petronas Yamahas of Valentino Rossi and Andrea Dovizioso propped up the timesheet in 20th and 21st.

The track has continued to dry since FP1 but further rain is a threat throughout the Austin weekend.