Valentino Rossi was pleased with Ducati's pace after MotoGP free practice at Assen, but admitted that tyre wear over a race distance was again a concern.
Ducati struggled to make its tyres last in the preceding grand prix at Silverstone, where Rossi was a distant ninth and his team-mate Nicky Hayden fell back to seventh after a promising start.
Hayden was third in the Netherlands on Thursday, while Rossi was back in eighth but pleased to be within 0.4 seconds of pacesetter Ben Spies' Yamaha.
"Today went pretty well, especially in the afternoon. I'm eighth, but the gap to the front is only four tenths, which is a decent step forward for us," said Rossi.
The former champion said sustaining that speed in Saturday's race was his only worry.
"Now the bike works well with new tyres, but we have to keep working on our race pace," Rossi said. "Both Nicky and I start sliding a lot when the tyre is worn, so we have to slow down too much compared to the others.
"Tomorrow, in order to be more consistent and improve the pace, we must try to improve rear grip without losing it at the front. Anyway, today wasn't a bad start."