Ferrari's rivals are becoming concerned about the Italian team's power advantage after the Belgian Grand Prix proved beyond doubt that Maranello's engine is the class of the field.
In the past two years, Ferrari's V6 turbo hybrid has replaced Mercedes' as the class-leading power unit in Formula One. Developments throughout 2018 saw the team take a significant advantage that it has only extended with the development of its engine this year.
Combined with an extremely efficient aerodynamic package the Ferrari was as much as 15km/h faster on the straights than rivals Mercedes at the Belgian Grand Prix, and the car's straight-line speed advantage helped Charles Leclerc secure the team's first victory of the season on Sunday.
What's more, Ferrari's advantage came with its Phase 2 power unit that it introduced at the Spanish Grand Prix in May, while Mercedes was using its brand new Phase 3 engine for the first time at Spa. Combined with two failures for its customer teams -- the engine in Sergio Perez's Racing Point blew during Friday practice and Robert Kubica's Williams lost an engine in qualifying -- Mercedes team boss Toto Wolff has compared his team's plight to that of Red Bull at the start of the turbo-hybrid era when it was regularly being let down by Renault's lack of power and reliability.
"I know now a little bit how Red Bull felt in 2014 and 2015 when you are on the back foot on the straights," he said. "Not a good weekend.
"We introduced Phase 3 of our power unit and we had two failures on Checo's [Perez's] and Robert's cars which are not understood.
"It didn't compromise us massively, but it did a tiny bit. We were not taking any risks in the race [with engine modes] but it was certainly not a comfortable situation because the failures looked to be different and are not analysed of yet and understood."
Red Bull switched to Honda power units this year and team boss Christian Horner believes Mercedes, Honda and Renault are now fairly evenly matched behind Ferrari.
"Ferrari is the benchmark in the power unit department at the moment," he said. "They are doing an incredible job, their straight-line speed is awesome -- hugely impressive, particularly on Saturdays.
"But it seems to be, certainly the group behind between Mercedes, Honda and Renault, that finally we have some convergence in performance."
Ferrari's advantage is likely to be even greater at this weekend's Italian Grand Prix where engine power has the biggest influence on lap time anywhere on the F1 calendar. Wolff says there is no way Mercedes can make up the difference in Monza, especially as Ferrari is expected to introduce its Phase 3 power unit after its customer teams ran it for the first time in Spa.
"I don't think you can find 15km/h in the next five days," Wolff said. "But it is what it is, no complaining.
"We have just got to prepare for Monza the best we can, knowing that it is not a track that will suit us. It will favour Ferrari but we have got to do the best possible job.
"On the Sunday we are looking much closer, even on the high power circuits, so I still think that we have got to give it all we have to hopefully win the race in Monza."