SHANGHAI, Oct 8 (Reuters) - Ferrari's Felipe Massa could hold the key to the Formula One championship in his home Brazilian Grand Prix on Oct. 21, despite being out of the reckoning himself.

Massa won at Interlagos last year from pole position, becoming the first Brazilian to win his home race since the great Ayrton Senna in 1993.

He had been expected to play a supporting role in that race to team mate Michael Schumacher in the seven times champion's final race before retirement, but a problem in qualifying and then a puncture left the German too far back to be helped.

The same applies this year with Massa returning home for the final race of the season in which his main role will be to assist team mate and title contender Kimi Raikkonen, unless the Finn hits similar misfortune.

After winning Sunday's Chinese Grand Prix, Raikkonen has 100 points, seven behind McLaren's championship leader Lewis Hamilton and three adrift of the Briton's double world champion team mate Fernando Alonso.

EIGHTH WIN

That victory was the 200th in Ferrari's history and eighth in 16 races this year.

The Finn needs a Ferrari one-two in Brazil, with Massa riding shotgun in second place to shoot down Alonso's title hopes.

After that he will just have to hope for the best, with Hamilton still needing to finish only fifth to be sure of becoming the first rookie world champion as well as the youngest.

The nightmare for Hamilton would be if Alonso were to be winning with the two Ferraris between him and his Spanish team mate. In that case, he would have to get past them both.

A better scenario for the Briton would be if Alonso were to be sandwiched between the two Ferraris with Massa leading.

Another win for the Brazilian would then send the title Hamilton's way even if he finished fourth.

"If Kimi has a chance during the race to win the championship, I think it's very good for the team and I would
also be very happy to help the team," the Brazilian said on Sunday.

"If maybe Lewis or Fernando are in the middle and we have no chance, I will try to win the race."