With Lewis Hamilton locked in a tight championship fight against Max Verstappen, Ross Brawn believes Mercedes no longer have the same margin for error that they did when the battle was internal.
The Silver Arrows have been the team to beat since the switch to turbo-hybrid engines in 2014, winning all Drivers' and Constructors' titles since then.
Red Bull have mounted a serious threat to end that run the season, and Brawn reckons Mercedes don't have the cushion they enjoyed in years past, when the only threat to their dominance came from within the team itself.
"It's a measure of a World Champion in a World Championship team, that little glitches – such as Lewis hitting the wall in qualifying – look glaring because you make them so infrequently," Brawn wrote in his column for the official Formula 1 website.
"Mercedes and Lewis weren't on it in qualifying, at a track where they were expected to dominate given recent history.
"Friday practice showed they were much quicker on the long runs. It was all there for them to take advantage. So the fact it didn't go to plan shows that this is not a slam dunk for them.
"They're going to have to fight hard all the way to the end if they are going to win the championship. Fighting hard internally is different than fighting hard externally. When you're fighting hard internally, what's the worse that can happen? If one driver doesn't win, the other would do.
"They had years where it was Nico [Rosberg] or Lewis as there was no one to pick up the pieces if they didn't deliver. Mercedes had that cushion if they messed up. Now there is no cushion."
Hamilton now leads the championship by two points after his 100th career F1 win, however Brawn credited Verstappen for limiting the damage at Sochi thanks to a "masterclass" performance.
"Max is putting up a massive challenge for championship, he was fantastic on Sunday, delivering a masterclass in damage limitation to recover to second from last and while he lost the championship lead, he's only two points behind Lewis now," Brawn concluded.
Video: Why grid penalties could decide the F1 title fight
RacingNews365.com takes a look at how grid penalties could be a crucial factor in the intense title fight between Lewis Hamilton and Max Verstappen.