SHANGHAI (AP) As the Formula One circuit heads to Shanghai for the Chinese Grand Prix, it's no longer a safe bet that Mercedes will top the podium by the end of the weekend.
After a jubilant Sebastian Vettel emerged as the surprise winner for Ferrari at the Malaysian Grand Prix two weeks ago, a season once expected to be dominated by the silver cars of Mercedes could be shaping up to be far more competitive.
Mercedes came into the 2015 season as the team to beat following a dominant campaign last year that saw Lewis Hamilton and Nico Rosberg sweep to victory in 16 of 19 races. The only suspense was generated by the fight between the Mercedes teammates for the drivers' championship, which Hamilton eventually captured.
But Vettel showed in Malaysia that the rest of the field wasn't prepared to move aside.
The four-time world champion, in just his second race for Ferrari after leaving Red Bull, benefited from a blisteringly hot track that caused Mercedes' tires to degrade quickly, but Vettel's Ferrari car also showed improved pace over last year.
Mercedes team principal Toto Wolff said after the race it was the ''wake-up call that we needed.''
''Malaysia was a tough weekend,'' Hamilton said ahead of Sunday's Chinese GP. ''I think ultimately we made the best choices we could, but there is always room for improvement and we've been working hard to analyze everything for the next race.''
Hamilton, who captured the season-opening race in Australia and was second in Malaysia, will be hoping for a boost on a track where he's enjoyed considerable success. He's won the Chinese Grand Prix three times - more than any other driver - and finished on the podium six times overall.
''Shanghai is one of my favorite locations,'' Hamilton said. ''The circuit itself is a different challenge to Albert Park (in Australia) and Sepang (Malaysia), but it's one I really enjoy and it suits my driving style quite well.''
Mercedes technical chief Paddy Lowe said the team has spent the past two weeks trying to make improvements to the car, citing its most significant weakness as tire management during long runs. He said the team also addressed the car's aerodynamics.
''It is now clearer than ever that there is serious competition for this world championship, so we will continue to work flat out for performance gains,'' Lowe said.
The conditions in Shanghai should cause less tire degradation compared to Malaysia, with temperatures only expected to reach about 21 degrees Celsius (70 Fahrenheit) for the race on Sunday.
The other top teams will be looking to play catch-up after difficult starts to the year.
McLaren has struggled with a host of issues with its Honda engines and managed just one finish in the first two F1 races - Jenson Button's 11th place result in Melbourne. The team has acknowledged that the long straights in Shanghai will also make it tough to close the gap.
Still, new McLaren driver Fernando Alonso sounded upbeat about the car's progress since the start of the season.
''The steps we took between Australia and Malaysia were extremely impressive - it was a great feeling to be able to mix it with other cars and drivers, and I hope we can do more of the same in China,'' he said.
Red Bull has faced even more questions as French automaker Renault, which supplies engines to the team, has threatened to pull out of the sport if it doesn't see improvements on the track.
In an interview with Formula1.com on Monday, Helmut Marko, Red Bull's senior advisor, called the start of the season ''a catastrophe.'' The team's best finish has been Daniel Ricciardo's sixth place in Melbourne.
''We are significantly behind Mercedes. They clearly dominate,'' Marko said.
As for whether Renault could pull out, Marko said the carmaker is ''spending a lot of money on this power unit - not as much as Mercedes but a significant amount - and (is) confronted with the same issues that we have: their F1 involvement has to pay off.''
Red Bull won the drivers' and teams' championships from 2010-13 with Renault before the sport switched to V6 hybrid engines last year.