Formula 1 championship leader Lewis Hamilton believes Mercedes has "work to do" with its car to stay ahead of Sebastian Vettel and Ferrari in the title battle.
Hamilton extended his lead over Vettel to 34 points with second place in the Malaysian Grand Prix, helped by the Ferrari driver having to start from the back of the grid.
But Vettel's pace as he charged through to finish fourth, and the fact that Hamilton had no answer to the speed of race winner Max Verstappen, highlighted that Mercedes is going to face a challenge in the final five races of the season.
When asked about the championship situation with Vettel, Hamilton said: "I feel good but we have some work to do with the car.
"We didn't have the pace here this weekend. There are still races ahead, and some we can win, but we've got to keep pushing.
"I struggled on both sets [of tyre compound], the car was good in some places and in some others, the issues we have with the car are magnified.
"There is still work to do - but it is a fundamental issue with this year's car."
Verstappen made short work of Hamilton to take the lead in the early stages, and while the Mercedes was slow on the straights at that stage because his battery pack was de-rating, he conceded that it was unlikely he could have kept the Red Bull behind anyway.
"Big congrats to Max, he did a fantastic job today," said Hamilton. "The race was a tough one.
"Obviously they [Red Bull] had the upper hand on us today.
"I was having problems with de-rate at the beginning of the race and struggling with battery power.
"I went to defend but didn't want to risk it, so didn't completely close the door and be aggressive.
"At the end of the day Max had more pace than me, so it was going to be a struggle to stay ahead."