Mercedes have acknowledged the increased threat posed by Red Bull after Daniel Ricciardo's stunning pace in testing on Wednesday.
The Australian broke the unofficial lap record which had stood for 10 years around the Circuit de Barcelona-Catalunya with a 1m18.047s on the Hypersoft tyre, finishing a third of a second clear of Lewis Hamilton, though the world champion's best would be on the slightly harder Ultrasoft.
Offering an assessment of how the top three teams were shaping up, motorsport boss Toto Wolff singled out the Milton Keynes outfit as becoming regular contenders in 2018 rather than only excelling on downforce-orientated circuits.
"What we have seen from Red Bull is that they have a very strong package," the Austrian said to Sky Sports. "I think will be very much in the game for race wins and the championship itself.
"I think it will be all three of us [Ferrari included] against each other."
Asked if Mercedes remained confident of being ahead, Wolff added: "What we have seen is that even if it is the best case we are not in front by a lot, and if it is a worst case we are not far behind.
"Honestly, l am excited by the prospect of a tough battle."
As for Ricciardo himself, he also sees Red Bull in a more competitive position going into the new season, though still with work to do.
“I think that looking at it now, we are close,” said the 28-year-old.
“I still don’t know where Ferrari are, I’m quite confident Mercedes is probably just in front of us but Ferrari I’m not sure, but I think we’re going to be much closer than last year."
The five-time Grand Prix winner also topped the individual lap count on the second day of the final test in Spain, setting a total even he didn't expect.
“It looks pretty positive for now. Reliability is pretty solid, we had planned for 160/170 laps at the start of the day and I was like, “that’s optimistic”, but we did it," he said, ending with 165.
“Reliability is solid and the car is coming along."
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