Marc Marquez, who has a perfect 9-0 record to start the season, dominated practice on the opening day of the Indianapolis Grand Prix, with Honda teammate Dani Pedrosa also posting fast times.
Spaniard Marquez looks poised to widen the gap on his rivals as he has a commanding lead at the halfway point of the season in the championship standings with 225 points.
The Indianapolis Motor Speedway`s 16-turn, 4.16 kilometre (2.6 mile) track was made slick by rain as the riders got in their first practice sessions ahead of Sunday`s race.
"It was not so bad," Marquez said. "We came back from the holidays and had a slow start with the rain.
"I am happy, because in the afternoon we could do a lot more work."
Marquez said the damp conditions Friday made it difficult to get a proper read on the track, which organizers recently resurfaced.
"The track grip changes each time we go out, and we have to change the set up a lot. Hopefully we can get more dry track time tomorrow," he said.
This is the second of two US races in 2014 as international motorcycle racing looks to make inroads into the United States. The first race was held in Austin, Texas in April.
Times were much quicker in the second practice session Friday, especially for Marquez who posted the fastest lap of the day and was the only rider to go below 1:33 (1:32.882).
Pedrosa used Friday`s practice to experiment with tyre combinations on the new track surface.
"We were able to progress a lot in the afternoon and tried out all the tyres," Pedrosa said. "But we still need to work to see what the pace will be like and find the limits of the track.
"Today the track conditions improved the more laps we all put in, because the asphalt cleaned up and gave us much more grip.
"On Saturday we will work on finding the limits and getting a good tyre combination for Sunday`s race."
MotoGP riders are back on the track Saturday for two practices followed by qualifying.