The Spaniard was pushed to the limit by Mexico's Sergio Perez, whose mistake on lap 50 arguably cost him a maiden race win for Sauber.

Perez, a member of Ferrari's young driver academy and linked with taking up the underperforming Felipe Massa's seat, claimed second place, collecting more points in this one race than he did throughout all of last season.

In a Ferrari that has so far been poor by the team's usual high standards, Alonso's win means he now leads the championship by five points from McLaren's Lewis Hamilton, who was forced to settle for third place after starting from pole for the second successive race.

No rain had fallen on Sepang since Thursday, ensuring practice and qualifying remained dry, however, 20 minutes prior to the start it decided to make an appearance.

It was only light at first, with all teams bar HRT switching to intermediate Pirelli tyres - with more of a groove to cope with the conditions - whilst the Spanish marque opted for extremes.

At least there was no safety car start, and when the red lights disappeared Hamilton made amends for his poor effort in Australia with a clean getaway, keeping compatriot Jenson Button behind him.

But over the opening laps the rain steadily grew in intensity, forcing virtually all drivers to make the move on to extremes.

Come the end of lap six, race director Charlie Whiting sent out the safety car, and on lap nine opted to suspend the race as it had clearly become too dangerous to continue.

At that point the field had been reduced to 23 cars, with Lotus' Romain Grosjean spinning into the gravel on lap four, and that after colliding with Michael Schumacher early on lap one.

From his highest grid position of third since coming out of retirement to join Mercedes ahead of the 2010 campaign, the 43-year-old was sent plummeting to 16th at that point.

The weather resulted in the 50-minute delay before the grand prix resumed again behind the safety car and with all cars instructed to be on wet tyres.

Initially there were four laps behind the safety car up until the end of lap 13, and immediately Button made the call to dive into the pits to take on inters, as did a number of others.

As with previous astute decisions in the past it appeared to be the right call.

Although emerging just behind Alonso, Button had done enough to get ahead of Hamilton, but not for long as on lap 15 he collided with the HRT of Narain Karthikeyan, losing the right end of his front wing.

It necessitated another stop, arguably robbing him of heat from his tyres because it was not long before he complained he could not get them to work, resulting in a fourth trip into the pits after 24 laps.

As the race then unfolded it appeared at one stage as if Alonso would go on to comfortably take the chequered flag, only for the remarkable Perez to close to within 1.3secs after 40 laps.

At that point the call was being made for teams to move their drivers on to dry tyres, and whilst Alonso did so, Perez stayed out - the team's error on that occasion.

Clearly quicker than the Ferrari, Perez closed to within 0.5secs at one stage, but then came his mistake, running wide at turn 14 and that was enough to ease the pressure on Alonso and give him the win.

Behind the top three Red Bull's Mark Webber was fourth for the second consecutive race, followed by Lotus' Kimi Raikkonen and Williams' Bruno Senna, a career-high result of sixth.

Force India's Paul di Resta grabbed seventh ahead of Jean-Eric Vergne for Toro Rosso, Nico Hulkenberg in his Force India, and then Schumacher.

A blown tyre after colliding with Karthikeyan a few laps from home robbed Vettel of points as he finished 11th, whilst Button was down in 14th, the race in stark contrast to his win Down Under seven days ago.

Alonso admitted his win was "a big surprise", but knows there is more work ahead as it was not representative of their current performance.

"We weren't competitive here nor in Australia," said Alonso.

"Our goal is to score as many points as possible and today we've scored 25, so an unbelievable result for the team.

"We kept calm in extreme conditions, and congratulations to the team. They deserve this result.

"But nothing changes for us to be honest. We're in a position we don't want, fighting to get into Q3 and fighting to score points rather than victories.

"These first two races are positive, and going into the next few races there is stuff coming to improve the car, so we will see."

As for Perez, he appreciated he should have been celebrating the win as he said: "I was catching Fernando towards the end.

"It was not easy, and then I ran wide, touched the kerb went into the wet and I lost the win, probably

"But the team has done an incredible job. I'm very happy for them."

Opposed to last week's unhappiness at third, on this occasion Hamilton declared himself "satisfied".

"We would love to have had more points this weekend," said Hamilton.

"But I can't complain, I'm on the podium, I stayed out of trouble with the conditions constantly changing."