SUZUKA, Japan -- Lewis Hamilton is wary of how much potential performance Ferrari's latest upgrades could deliver at this weekend's Japanese Grand Prix if Sebastian Vettel's car runs without problems.

Ferrari's true pace has been masked at the last two rounds after Vettel and teammate Kimi Raikkonen both crashed out of the Singapore Grand Prix and then had their race weekends ruined by engine problems in Malaysia.

When the Ferrari has been running without issues at the last two grands prix it has shown impressive one-lap and race pace, while Mercedes has struggled for outright performance despite capitalising on Ferrari's misfortune.

Hamilton is confident the track layout and cooler conditions in Japan will suit Mercedes more than the heat of Singapore and Malaysia, but is not ruling out Vettel and Ferrari making a comeback.

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"I think our car will be in a much better position [in Japan], but Ferrari brought quite a big upgrade to the last race so it will be interesting to see that properly unleashed," he said. "I think with Sebastian having a penalty [of starting from the back of the grid] in the last race, we saw him come through but we didn't get to see him really run at the front, so that's exciting and I just hope that we have enough strength to be able to fight that. And also the Red Bulls are coming up.

"We've got improvements coming this weekend so hopefully that gives us a stronger platform just to battle. The whole exciting thing is to have the opportunity to fight, to remain in the fight."

With just five races remaining, Hamilton leads Vettel by 34 points in the drivers' standings but insists he is not yet thinking about the prospect of becoming a four-time world champion.

"I'm definitely under no illusion -- I don't feel comfortable at all," he added. "It's not that I'm not at ease, either, I just want to win this thing and I might have the nail a little bit in but I've got to keep hammering it.

"It's not done until there's nothing more to push in. There's so many points available, we've seen other years where the pendulum can just swing, so hoping that if it starts to swing we have enough force to push it the other way."

If Hamilton leaves Suzuka with a 29-point lead over Vettel, he will only need to finish second at the remaining four rounds to secure the championship -- regardless of Vettel's results. After last year's Japanese Grand Prix, Hamilton found himself on the opposite end of a similar equation in his title battle with teammate Nico Rosberg and, despite winning the remaining four races, lost the championship due to Rosberg's four second place finishes.

But Hamilton says he still feels like he is hunting this year's title rather than defending it.

"I just want to win every weekend," he said. "Somebody mentioned something about Nico only wanting to finish second [at the final races of last year] but he was qualifying to get pole, he wasn't qualifying to get second position. People looked upon it as if he drove to finish second, but he couldn't get by to win the race because I was gone!

"For me, the goal is to continue to win races even if I don't have to win another grand prix through the rest of the year. That's the best way because I am still hunting it, I am not defending it. I'm still hunting and chasing that championship and until that last flag and until I've actually got it sewn up, then that's what I've got to keep doing."