With a hot sun pushing temperatures up to 30ºC, 50ºC on the track, the Repsol rider was the fastest in the opening practice session, despite an early crash, and still carrying a shoulder injury from two weeks ago in Brno.Márquez, who started cautiously in order to ride in the Derbi RSA engine, went down after just 15 minutes, when the left-hand bend entering the straight closed him off. This was a small error from the young Repsol rider, after going over a slightly dirty area of the track at bend 16. After a quick check over the bike in boxes, Marquez was back on the circuit to complete the rest of the session without further mishap.Márquez progressively fine-tuned the bike’s setup as he increased the pace. At the half hour mark, he was among the five fastest, and with 15 minutes left he was in first place, clocking in under 1′ 50”. After the last stop in boxes, the Repsol rider continued to improve, setting a time of 1.49.452, which is yet to be beaten. So, Márquez has put in the best time in his first session at the US track.Marc Marquez says: "At the beginning of practice, I had a bit of a scare which shouldn’t really have happened, as I came out of boxes quite confident after having gone round the track, then I went down on the first lap, which wasn’t even timed. The track was dirty and I didn’t expect it to slip so much. What’s important is that I’m OK, and so is the bike, and I could continue practice without problems.""In the end, what matters is that I was comfortable on the last laps and the most important thing is not first place, but that we know we can still improve a lot, because we still need to work the setup a lot going into tomorrow. I fell on the bad shoulder, a fast fall that I really wasn’t expecting, but the shoulder has reacted well. It doesn’t hurt, but I lack a bit of strength, which is perhaps what I will notice in the race, because on the final practice laps I started to notice it a bit."