Valentino Rossi spent much of his penultimate race as a MotoGP rider battling with younger brother Luca Marini at Portimao on Sunday.

A poor start meant Marini dropped behind 16th place Rossi on the opening lap, but was able to overtake the Petronas Yamaha rider at half race distance.

Rossi then stuck with the rookie and was poised to retaliate when the red flags were raised with three laps to go due to an incident for Miguel Oliveira and Iker Lecuona.

That left Marini in 12th and Rossi as the top Yamaha rider in 13th, after new world champion Fabio Quartararo's fall. Crossing the line behind Rossi were team-mate Andrea Dovizioso, Honda test rider Stefan Bradl, Aprilia's Maverick Vinales and Monster Yamaha's Franco  Morbidelli.

"The first target was try to arrive in the points," Rossi said. "The race was very fast and I had a good pace during all the race compared to practice. I was able to make some overtaking and stay behind my brother, who was a bit faster.

"So we did a good race together and at the end I was able to recover and I can try to attack him but then we had the red flag. I have some points where I was faster than Luca. But in the last part, Luca was a bit faster than me so I don’t know if I'm able to overtake.

"Without the red flag I can try for one position more but it's okay like this."

Prior this season, a 13th place finish for Rossi would have been cause for an inquest.

However, the nine-time world champion has come to terms with what has been a tough final campaign as he heads straight for Valencia and the last race of his illustrious career.

"For me the results are very important, if you are strong and you can fight for the podium and top five. This season was tough for me. I expected and I hoped to be a bit stronger, so I think [retirement] is the right choice. But I'm okay, I'm quiet and it's just one race to go," he said.

"From one side it's a bit sad because I know that from next year my life will change but from the other side it's okay because anyway it's a long season and it's very difficult, very tough, the level is very high.

"But I feel good. Valencia is a difficult track for me but I want to try the maximum, try to stay concentrated to take some points also there."

While Rossi's results this season have been the worst of his grand prix career, his time margin to the front has rarely been more than one-second a lap.

During the weekend, former rival Casey Stoner said that he thought the amount of electronic assistance should be reduced to try and increase mistakes under acceleration, allowing more passing.

"This aspect is one of the things that changed more from the time of Casey, ten years ago," Rossi said. "Imagine that the last place lap time in the race is 0.9s slower than Pecco that made the fastest lap.

"In qualifying, I take 0.9 and I was P16. So the bikes like they are now helps a lot every rider to be more consistent, with electronics.

"It's also true that all the riders are better prepared for the races now and [almost] everyone in MotoGP has been a world champion. So even last place is a f**king [good] rider, you know!

"Under one point of view I agree with Casey, but this is the modern MotoGP, it's like this [with electronics].

"I think during all these years Dorna and everybody worked a lot to have a very balanced grid, to have less difference between the factory bikes and non-factory bikes and I think they have arrived at a good result under this point of view."

Excluding the opening lap, the difference between the fastest and slowest race laps by winner and VR46 protegee Francesco Bagnaia was just 0.692s!