Things did not start well when the session was delayed for over an hour in order to clean a large film of oil laid down in the preceding Moto3 practice.
When the session did finally commence, there was hardly a clamour to go out due to the conditions. Several wet patches meant slicks were not an option, but equally stretches of dry asphalt meant wets could only handle short stints before being destroyed.
That helped convince all of the frontrunners to skip the session, with only nine riders - and only four prototype bikes - setting times.
Of the nine Hayden was comfortably fastest for Ducati, eight tenths of a second ahead of team-mate Valentino Rossi, who claimed his first dry podium for the team last time out at Misano.
The two satellite Ducatis of Hector Barbera (Pramac) and Karel Abraham (Cardion) also ventured out, but very briefly.
Barbera, involved in the crash which wiped out Dani Pedrosa at Misano, ended the session fifth fastest, 3.8 seconds down on Hayden. Abraham was ninth overall, seven seconds down the road.
Aspar's Aleix Espargaro was the top CRT rider in third, 2.4s down on Hayden.