MEXICO CITY, Oct 31 - Mercedes' Kimi Antonelli said he had been driving with more tension than usual as the 20-year-old prepared for a Mexican Grand Prix that could make him Formula One's youngest world champion.

The Italian is set to line up fourth on the grid at the Autodromo Hermanos Rodriguez on Sunday and needs only to finish ninth to secure the title, becoming Italy's first champion since Alberto Ascari in 1953.

"Definitely, I've been a bit more tense than usual, especially when you keep hearing, wherever you go, any time of the day, the same thing," Antonelli told reporters on Saturday.

Antonelli, who was fifth fastest in qualifying but gained a place after Red Bull's Max Verstappen received a grid penalty, said the prospect of the title being treated as a formality had been difficult to ignore.

"People telling that it's already done," he said. "Knowing myself, I've been trying to block as much as possible this noise, but it hasn't been easy."

Antonelli's closest title rival is Mercedes teammate George Russell, who qualified second, 123 points behind with only 100 remaining to be won after this weekend.

Russell or Ferrari's Lewis Hamilton, who secured the pole position, must win on Sunday to delay Antonelli's coronation.

ILLNESS PROBLEMS

The championship leader has also been recovering from illness, having suffered a high fever and stomach problems on Thursday.

"I still haven't recovered completely," Antonelli said, adding his energy levels were low and he had not been sleeping well. "It's not an excuse, but for sure it hasn't been my finest (drive)."

Antonelli said he felt competitive in the second phase of qualifying on used tyres but struggled to produce a clean lap on fresh rubber in the final shootout.

His starting position nevertheless gives him a strong opportunity to secure the points he needs, although Turn One in Mexico City can create a chaotic opening lap.

"It's going to be important to get off the line well," he said. "Turn One is always very tricky. But I think if we get a good start, we have a good chance to move forward."

Antonelli said he would try to rest before Sunday, with his family having arrived in Mexico City.

"Just going to try to disconnect as much as possible, good sleep, and then ready for tomorrow," he added. REUTERS