Shanghai: Nico Rosberg's victory at the Chinese Grand Prix made it three different winners in three races so far this season -- but not one of them has been the Red Bull of reigning champion Sebastian Vettel.

It is a dramatic decline in fortunes for a driver and a team which at the same stage last season had bagged two Grand Prix victories and three pole positions, as Vettel rampaged his way to a second world title on the spin.

Fast forward 12 months and it's a dramatically different picture.

Germany's Vettel, 24, said he was pleased to finish fifth in Shanghai on Sunday, after the indignity of starting a lowly 11th on the grid.

His frustrating weekend reached another low when he made a poor start to the race, falling to 15th, before slowly making his way through the unfamiliar territory of midfield.

"The first lap wasn't great, but with the strategy we managed to come back," said Vettel, who opted to use the old exhaust settings because he had not been happy with the set-up of the car for the first two races.

"I think the weekend was good for us," he insisted.

Christian Horner, Red Bull's team principal, was also putting a brave face on a result that leaves the team trailing rivals McLaren in the constructors' championship, while Vettel is languishing in fifth in the drivers' standings.

"Our race pace was pretty strong and we got amongst the McLarens," said Horner.

"Unfortunately, the front left tyre on Sebastian's car took a real hammering, possibly behind Kimi (Raikkonen), and he didn't have anything left tyre-wise by the end of the race.

"But nonetheless, having been 15th on the first lap, fifth is still a strong result."

Unlike his imperious past two seasons, Vettel has been consistently slower than team-mate Mark Webber, who is on a different car set-up and appears to have the edge, despite Vettel's second place in the season-opener in Melbourne.

Australia's Webber sits fourth in the drivers' standings. Britain's Lewis Hamilton is top, ahead of McLaren team-mate and Melbourne winner Jenson Button and Ferrari's Fernando Alonso, victorious in Malaysia.

The usually affable and level-headed Vettel denied in Shanghai that he was struggling to get used to the idea of having to scrap it out with the rest just for a place on the podium.

But he lashed out after missing out on the points last month in Malaysia, where he came home in a distinctly average 11th place, suggesting the pressure of competing in an inferior car was putting a strain on him.

He blamed HRT's Narain Karthikeyan after they had a coming together late in that race, and later branded the Indian "an idiot". Karthikeyan retorted by saying that Vettel was "a cry baby".

Experts say that Red Bull and Vettel are suffering more than many of the other teams from a rule change that banned exhaust-blown diffusers.

In contrast, Vettel's compatriot Rosberg and his speedy Mercedes appear to be going in the opposite direction after the German claimed the first Grand Prix win of his career.

The Mercedes garage erupted in joy at his convincing victory -- which was also Mercedes' first GP win since 1955 -- but Rosberg was keen not to get too carried away, with the controversial Bahrain race going ahead on Sunday.

"I had a great race today but that doesn't mean it's going to be like that at every race," he cautioned.

"We still need to push hard and continue progressing. Bahrain could be a little bit of a different story again. We need to wait and see. It's difficult to predict.

"I couldn't have predicted today so we'll just take it as it comes, but for sure I'm looking forward to what's to come because we're looking much stronger."

The only sour point was the retirement of team-mate Michael Schumacher with just a quarter of the race gone when he exited the pit before one of his wheels could be properly fixed and had to bow out.