After another full-on fight between the two champions in Turkey, Alonso left Istanbul with a 12-point lead but recognising that anything could happen in the last four races.

The tyres, said the world champion, could make or break both men's dreams.

"I think we are in Michelin and Bridgestone's hands because at the end of the day, I think the cars are at their maximum development now," the Spaniard said.

"In the last part of the championship, I don't think you can find extra tenths or two tenths (of a second) in the car, while the tyres can give you more than half a second.

"So I think that...the tyres will be the deciding point in the championship."

Both Michelin-shod Renault and Bridgestone-equipped Ferrari have a busy test schedule over the coming week before the Italian Grand Prix, Ferrari's home race, at Monza.

After Monza there will be two more tests for Renault while Ferrari are likely to be using their private Fiorano test facility to the maximum.

Renault have a more powerful engine and new developments coming in for Monza and remain confident, despite their constructors' lead being whittled down to two points.

REALLY CLOSE

"It's still really close, we always said it would be," said the team's head of engineering Pat Symonds as he left the Istanbul Park circuit on Sunday.

"I'm really pleased we are getting some testing in because it's been a struggle for the last few weeks, particularly with the mass damper coming off and everything.

"Michelin have got a hell of a programme for next week so there's a lot to do there and I think when we finish that programme we will have a better idea of where we stand. But I think it's going to be close in every race."

Alonso finished second in Turkey, with Schumacher third after a safety car interlude allowed the Spaniard to get past the seven-times champion in the pits in a race won by Ferrari's Felipe Massa.

The result was a boost for both Alonso and Renault, deprived of a performance-enhancing 'mass damper' system after the governing body declared it illegal.

Renault showed they remained competitive without it, although they also had fate and human error to thank for Alonso's second place.

Had the safety car not come out when it did, there is every reason to suspect that Massa would have let Schumacher past to lead home a Ferrari one-two. That would have slashed Alonso's advantage to six points.

Had Schumacher not run wide after the first stop, losing precious time, he might have been able to get back in front of Alonso at the second stop with a similar outcome.

Equally, Alonso could feel a wheelnut problem robbed him of the previous race in Hungary when he was leading as Schumacher struggled.

"If I hadn't had the problem in Hungary with the tyre, probably we are talking about 22 points (advantage), which is quite good with four races to go," he said.

"You can increase the gap or lose everything very quickly these days in these races so it's not comfortable any more...this week we did it, we got in front of one of the Ferraris while in the last races we were too far behind.

"At Hockenheim, I was a minute behind them."