Lewis Hamilton said he believes Ferrari may have the quickest car with three days remaining of Formula 1’s pre-season testing programme.
Williams driver Felipe Massa set the pace on the first day of the final test but Ferrari’s Sebastian Vettel was less than 0.2 seconds behind on a slower tyre.
Hamilton was fourth fastest for Mercedes, 0.5secs behind the German.
“Ferrari are possibly the favourites,” Hamilton said.
“We can’t take our eyes off them they are doing such a great job.
“And Red Bull look like they’re going quite quick today. It is going to be close at the first race for sure.”
Red Bull’s Daniel Ricciardo was second fastest overall on Tuesday, but set his time while using the fastest ultra-soft tyre which no other driver did.
Who is really quickest?
It is notoriously difficult accurately to predict competitiveness from pre-season testing because there are so many variables.
But Ferrari have impressed onlookers and rival teams this year so far with their consistently fast times, while not using either of the two softest types of tyre.
Vettel continued this form on Tuesday, lapping just 0.18secs slower than Massa, who was using a tyre that Pirelli reckons to be about 0.8secs faster.
Red Bull also appeared competitive, Ricciardo swapping times with Vettel and Hamilton during the morning session.
Hamilton said he had had a difficult morning before handing over to new team-mate Valtteri Bottas for the afternoon.
“It didn’t feel spectacular this morning,” he said, “but we had some issues with tyre temps and with some floor damage so I sacrificed some of my time so Valtteri could run this afternoon.”
More problems for McLaren
Meanwhile, McLaren and engine partner Honda suffered another blow in a troubled pre-season programme.
Honda decided to change the engine in the car Stoffel Vandoorne was driving when they discovered an electrical problem after just 34 laps.
It is the latest in a series of problems with Honda’s newly redesigned engine.
Honda has had three engine failures in the course of five days of testing so far. The Japanese company has not revealed how many engines it has gone through – a spokesman saying it has used “a mixture, and some have been used on multiple days” – but it is believed to be at least five.
Vandoorne ended the day 10th fastest, 2.8secs off the pace.
McLaren racing director Eric Boullier admitted relations between the two partners were under “maximum” strain.
He added: “The pressure is obviously huge and obviously we put the maximum pressure on all of our relationship with Honda, and the same for them.
“We cannot put a footstep wrong. We need to be able to deliver the best car as well, so this is both sides.”
He said he hoped a new specification of Honda engine to be introduced before the end of this week’s test would solve “part of this problem – or most of this problem”.
And he insisted McLaren were not considering ending its contract with Honda, which is in the third of 10 years.
“We have a contract in place,” said Boullier. “We don’t even obviously think about it, because there is a contract between us, a long term contract, and we want to build on it even if it is not ideal times.”
Final pre-season test, day one, fastest times
1 Felipe Massa (Brz) Williams 1:19.726 **
2 Daniel Ricciardo (Aus) Red Bull 1:19.900 ***
3 Sebastian Vettel (Ger) Ferrari 1:19.906 *
4 Lewis Hamilton (GB) Mercedes 1:20.456 *
5 Valtteri Bottas (Fin) Mercedes 1:20.924 *
6 Esteban Ocon (Fra) Force India 1:21.347 **
7 Nico Hulkenberg (Ger) Renault 1:21.989 *
8 Kevin Magnussen (Den) Haas 1:21.676 *
9 Daniil Kvyat (Spa) Toro Rosso 1:21.743 *
10 Stoffel Vandoorne (Bel) McLaren 1:22.537 *
11 Pascal Wehrlein (Ger) Sauber 1:23.336 *
12 Marcus Ericsson (Swe) Sauber 1:23.630 *
13 Jolyon Palmer (GB) Renault 1:24.790 *
* = time set on soft tyre; ** = super-soft tyre; *** = ultra-soft tyre. Others medium