Lewis Hamilton claims Mercedes has made no progress compared to their previous season, after finishing an "exhausting" Japanese Grand Prix.
The Mercedes driver finished fifth ahead of Singapore winner Carlos Sainz, after Ferrari made a mistake with its tyre strategy in the final stint of the race.
Hamilton worked his way up from seventh on the grid on a three-stop strategy, with Mercedes electing to swap cars midway through the race while George Russell was on a one-stop.
"I'm exhausted for one. It's fighting the car with absolutely everything I have, to get as high up as possible and get ahead of Ferrari, which had an upgrade this week," he told Sky Sports.
"It was it was a hell of a fight and race trying to hold on to the Constructors' title, I scored the most points for the team."
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Hamilton: The car is a handful
The problems that the team experienced with the W13 are well documented, but Hamilton feels they have made little progress in the last 12 months after similar issues arose during the race.
"I know how important it is for everyone in the background, back at the the factories and so I have given it absolutely everything," he added.
"But it's tough on weekends like this, particularly with a car is such a handful.
"Feeling-wise it's the same as last year; bouncing and sliding. So that's tough, given how much work we've done to progress and we're not any closer to the front.
"But we did get ahead of one of the Ferraris, which was great teamwork and great work from the guys in the pitstop and strategy."