MotoGP world champion Valentino Rossi was surprised by the pace of race winner Dani Pedrosa in Sunday's US Grand Prix - and even more surprised to find himself zeroing-in on the Spaniard with just a few corners to go.

“The first half of the race was quite difficult because we weren't at 100% today. I didn't expect Dani to be so fast but he was very strong and there wasn't much I could do to go with him!” said Rossi.

While Pedrosa blasted from fourth on the grid to first and began to pull away early in the race, Rossi lost and then regained second from Casey Stoner, before being hunted down by injured Fiat Yamaha team-mate Jorge Lorenzo.

Rossi couldn't keep the young Spaniard at bay, but when the #99 tried to outbrake Rossi with five laps to go, he ran wide. Rossi then put his head down to secure second over his nearest title rival, and found that he was rapidly catching Pedrosa in the process.

“The last ten laps were very exciting because Lorenzo was pushing me so hard that I had to really make another step and then Dani slowed down and suddenly he was right in front of me!” said Rossi.

The slowing Repsol Honda rider began the last lap over 1.5sec in front of Rossi, but the Italian soon ate up most of that advantage and tried his luck with an inside move at the final hairpin.

“I thought there was a chance to pass on the final corner but unfortunately I was just too far off and it was too much of a risk,” said Rossi, who crossed the line 0.344sec behind Pedrosa.

“Second is good today because we were not in perfect shape here, we missed something in the setting and this is always a hard track anyway, so we have to be happy with these 20 points.”

After round eight of 17, Rossi is nine points ahead of Lorenzo and 16 ahead of Stoner, who finished fourth for Ducati on Sunday.