Sixth place finish at Valencia a shock for Yamaha stand-in Katsuyuki Nakasuga

Nakasuga, one of Yamaha's factory test riders, was drafted in to deputise for Jorge Lorenzo for the final two races of the MotoGP season after the 2010 champion suffered a hand injury at Phillip Island.

The Sepang race was cancelled after Marco Simoncelli's fatal accident, but in today's Valencia GP Nakasuga took advantage of the first-corner carnage to come through from 16th on the grid to sixth, winning a long battle with Tech 3 Yamaha substitute rider Josh Hayes as both beat five full-time MotoGP riders.

"I was really surprised with sixth position in the race," said Nakasuga.

"In the beginning I was very nervous because of the weather conditions so my main target was to complete the race. I am used to Japanese races which only last 30 minutes so I was worried that I might not be able to keep my concentration for nearly double the time.

"Finally I'm very happy, the last five laps were quite risky because it wasn't easy to go faster but I had nothing to lose so I wanted to push as hard as I could.

"It's been amazing to experiment with a real grand prix race, not only can I use this for future development riding but I'm very pleased with the good result. The weather maybe helped me, but I am happy and enjoying the moment."

Team manager Wilco Zeelenberg said Nakasuga's result exceeded Yamaha's expectations as well.

"That was a very surprising race but very exciting as well," he said, after also seeing lead rider Ben Spies miss out on victory by just 0.015 seconds as Casey Stoner pipped him on the line.

"We are very happy with the results; Nakasuga-san's sixth position is fantastic. 30 laps in dry and wet conditions are very difficult when you have to push. To finish in front of regular GP riders is very good."