Fernando Alonso believes Michael Schumacher's San Marino Grand Prix win proves Formula One's most successful driver is a genuine world championship threat again.

Schumacher held off Enstone's Renault F1 team world champion for 30 nerve-wracking laps at Imola to claim his first real win since October 2004.

Those ten points have shot Schumacher up to second in the standings, 15 points behind Alonso, who expects a more sustained challenge from Ferrari than their meek title defence last year.

He said: "Michael for sure will be a contender and a big rival at the end of the championship, but he is not the only one.

"Both McLarens will be there and I hope Giancarlo Fisichella will be at the end fighting. It can be more than two or three drivers at the end of the championship."

A slow spell midway through the race saw Alonso catch Schumacher and set up a repeat of last season's tense finale, when the roles were reversed and the Spaniard clung on to win.

Schumacher kept his nerve to win and end a victory drought dating back to his last title-winning season, discounting the six-car parade at Indianapolis last year.

Despite being beaten, Alonso was content with the result and still believes Renault hold an advantage over their rivals.

"As far as me being competitive, this track was never a good track for us, but we were still the fastest car on the track," he added.

"I am very confident for the next races and the championship - it looks a little bit better."

Schumacher feels Ferrari's long-awaited resurgence is just reward for their hard work so far this season.

The former world champions started well with second place for Schumacher in Bahrain but their challenge was derailed with disappointments in Malaysia and Australia.

They have regrouped and Schumacher is convinced he has a car capable of threatening Alonso's Renault.

He said: "The championship had not really gone away, honestly, even with two difficult races. It's looking better now, but there's a long way to go. We should be pretty good from now on. It's getting very close between the top teams.

"It is always the same at the end of the day whoever maximises their opportunities will be in front."

One team who certainly did not maximise their opportunity at Imola was Honda, who saw Jenson Button lose third place due to a pit stop blunder.

Button was told to leave the pits before his crew had finished refuelling and he lost 16 seconds after ripping the fuel nozzle from its line.

That delay meant the Englishman had to settle for seventh place when he felt he had the beating of third-placed Juan Pablo Montoya's McLaren and Felipe Massa's Ferrari, in fourth.

Kimi Raikkonen was fifth in the other McLaren while Mark Webber was sixth for Williams. Fisichella took the final point for Renault but David Coulthard retired after a driveshaft problem on his Red Bull.