Alberto Puig's team, which previously ran Hondas, spent much of the morning examining its new Austrian-built motorcycles, before both Simon and Rabat emerged on track.
18-year-old Rabat, a Repsol Honda rider for the past two years, completed 74 laps and set the fifth fastest lap time, 1.2secs behind Aprilia's world champion Gabor Talmacsi.
"I was dying to get on this new bike," enthused the Spaniard. "I was testing the whole day, trying to get used to it as it is different to the Honda and we had to change a few things so that I could get more and more comfortable.
"The riding position is a little different, but it is something that we will have to get used to quickly," added the 2007 podium finisher. "In general everything was positive, although we will have to improve quite a lot, above all some aspects of the chassis, as I have not got the right compromise between riding comfortably and entering curves with the right amount of confidence. The bike is quite a lot faster [than the Honda]."
Marc Márquez, Rabat's new team-mate following the departure of Bradley Smith to Aprilia, has not yet joined the team as he is participating in the Spanish Championship, with one race still to go.
Meanwhile, Simon was ninth fastest on the quarter-litre machine, 1.7secs behind KTM factory rider Hiroshi Aoyama.
"This was my first time on the KTM. We began a little late, several modifications had to be made to the bike, and so the mechanics could learn how the new bike works," he said. "I went off the track once when I was trying to get used to it, and then I realised that the engine power is higher than on last year's bike.
"On the other hand at the moment I have a few problems with the chassis, mainly when entering corners. But we are going to be changing my position on the bike since I am not totally comfortable. For the first day obviously the times are bit slow, but right now I had not thought about that too much. Tomorrow I will carry on getting used to the bike's characteristics, above all the chassis," concluded Simon, who rode a 125cc KTM during 2005 and 2006.
