Dovizioso tops wet Austin practice

As steady rain fell, the day's programme was delayed by 50 minutes after an insufficient number of officials arrived, and after just 12 minutes the session was red flagged when a dog found its way onto the circuit.

When running resumed 20 minutes later, Marquez wasted little time stamping his authority on proceedings, unseating Yonny Hernandez - who was the first rider into the 2m22s bracket - at the top of the order.

He then improved again to a 2m20.617s, and was more than a second clear of the field before his challengers emerged in the final 10 minutes.

Brit Scott Redding jumped up the order and with six minutes remaining was just 0.030 seconds behind Marquez.

The two-time MotoGP champion improved to rebuild his advantage, only for Dovizioso to jump up to second, 0.042s shy.

Marquez went faster again with two minutes remaining and his 2m19.864s lap looked decisive, until Dovizioso managed a 2m19.402s after the chequered flag, with both riders surviving late moments in the challenging conditions.

Redding ended the session third, 1.085s behind Dovizioso, while Qatar winner Valentino Rossi was fourth ahead of Danilo Petrucci and Tech 3 Yamaha pair Bradley Smith and Pol Espargaro.

On a new Honda chassis, Cal Crutchlow was ninth and Jorge Lorenzo rounded out the top 10 on his factory Yamaha.

After suffering helmet problems in the season opener, Lorenzo struggled with steam inside his visor and stopped mid-session for holes to be drilled to combat the problem.

Deputising for Dani Pedrosa, Hiroshi Aoyama was 12th, while the only local rider in the field, Nicky Hayden was 15th to start his 200th grand prix weekend.

Suzuki rider Maverick Vinales, Austin's 2014 Moto2 winner, recorded the only real incident of the session, falling at Turn 2 with five minutes remaining.