Valentino Rossi said that topping Friday practice at Motegi was an important morale boost after his main rival Casey Stoner had been fastest in every session in the Qatar season opener.
Ducati rider Stoner was in front again for much of the afternoon in Japan, but Rossi managed to grab the top spot with his final lap.
"This is a very good start because we're at the top and this is very important," said the world champion.
"The conditions today were hard and it was difficult to reach the limit and work to the maximum with the bike and tires, but it looks like we have a good potential here so I am happy.
"It's important to be in front, even though it's only Friday, because in Qatar we were second in every session and really we don't like second so much; for sure first is much better."
Yamaha team boss Davide Brivio was also pleased to start the weekend in front, especially as the forecast suggests the weather will change tomorrow.
"It's nice to be back on top, even if it's only Friday," he said.
"It was always going to be very important to make the most of this session because there's a chance it could be the only dry one, so we wanted to try to explore a few different things. It went OK; we can definitely improve more but we have made a good start."
Rossi said he would be quite happy to see rain tomorrow because there has not yet been an opportunity to try the new control wets supplied by Bridgestone.
"Tomorrow it seems it may rain but we haven't had the chance to try the new Bridgestone rain tires yet so I think that this could be an important chance for us to understand how they are," he said. "It will be interesting and I hope they are good."