Sergio Perez says he didn't have the time to react to a late move from Lewis Hamilton, which is why his Japanese GP ended in the gravel.
Perez, who will replace Hamilton at McLaren next season, had an exciting tussle with the Mercedes-bound driver at the Suzuka track on Sunday.
Perez fired the first shot, overtaking Hamilton on lap seven when he dived down the inside when the Brit ran a bit wide.
However, after the first round of pit stops Perez was again behind Hamilton and attempted to overtake him on lap 20. But instead of making a move he beached his Sauber in the gravel.
"I was going to overtake him [Hamilton] there," Perez explained.
"He moved a little bit late and there was no time for me to go the other side. I went round but locked my rear and spun.
"There was nothing I could do and I went into the gravel."
His retirement cost the Mexican a solid points-haul as he had been running comfortably inside the top ten.
"Today was a very good position, I gave the team a good position and feel very sorry for them.
"It was my mistake and that is it."