SOCHI, Russia (AP) Sebastian Vettel and Ferrari have had the upper hand so far in Formula One.
They don't expect to have it against Lewis Hamilton this weekend at the Russian Grand Prix.
The long straights in Sochi suit Mercedes, which has won all three races to date around Olympic Park.
With two wins from three races, Vettel is seven points ahead of Hamilton in the standings, but expects that lead to come under pressure from the Mercedes drivers on Sunday.
''On paper, it's a very, very strong circuit for them,'' Vettel said. ''A lot of straights, a power-sensitive circuit, so we'll see, but there's also a lot of corners where I believe last year already the (Ferrari) car was very good.''
Vettel's wins in Australia and last time out in Bahrain have already disrupted the Mercedes dominance of the previous three seasons. Turning those promising signs into a serious title challenge over the remaining 17 races is a different proposition.
''We had a great start, yes. We're very happy about it, yes. But have we, you know, achieved anything yet? No,'' said Vettel, a four-time champion with his previous team Red Bull. ''Head down and full steam for this race.''
Hamilton said he was hoping for a ''counterattack'' in Russia, but warned that Mercedes' history of dominance in Sochi doesn't mean an easy win is on the cards.
''If we win, it's going to be earned, and we're here to earn it,'' he said. ''We're just going to have to drive the socks off the car.''
Hamilton and Vettel have beaten their respective teammates Valtteri Bottas and Kimi Raikkonen in all three races this season. As the title race takes shape, Bottas and Raikkonen face being forced to sacrifice their own opportunities to help a more successful teammate's title chances.
When Mercedes teammates Hamilton and Nico Rosberg fought for last year's title with other teams far behind, letting them fight it out on the track carried less of a risk. In 2017, Ferrari and Mercedes know that if one of their drivers fights his teammate, it could allow the other team to steal valuable points.
Raikkonen, a former champion who hasn't won a race since 2013, said he'd help Vettel's title hopes ''if it comes to that at the end of the year,'' but doesn't see himself as No. 2. Vettel said it was too early in the season to talk team orders.
At Mercedes, there's a stark contrast between Bottas and Rosberg, who had a fierce rivalry with Hamilton for years before winning the 2016 title and promptly retiring.
''Our job is to get maximum points (for the team). If I'm ordered to move over, I will,'' Bottas said. ''But I'm working to make sure I'm not in that position.''
No fan of team orders, Hamilton said Mercedes will order one of its drivers to let the other pass only in ''special circumstances,'' but added: ''Our approach is, the team needs to win.''
Bottas was ordered to let Hamilton, who was on fresher tires, pass in Bahrain so that the British driver could attack Vettel.
''Whilst it was very tough for him, he was a great gentleman about it,'' Hamilton said, adding he'd have done the same for Bottas if ordered to.
The Finn admitted he's still learning how to get the most out of the car after joining Mercedes in January at short notice when Rosberg announced his retirement.
''It's all about fine details in the fight between us and Ferrari and obviously it's also very close between teammates as well, so every little bit helps,'' Bottas said. ''These 100 days, I've never in my life learned so much.''
The only team capable of challenging Mercedes and Ferrari so far is Red Bull, which showed its potential with third in China for Max Verstappen.
However, reliability has stopped Red Bull gathering much momentum, with brake failure for Verstappen at the last race in Bahrain, and a fuel pressure issue for Daniel Ricciardo in Australia.
Ricciardo said he's hoping for ''a bit of a bullet'' when promised upgrades arrive at the next race in Spain. That could make the championship a ''three-way fight'' with Ferrari and McLaren, he added.