The 30-year-old Spaniard started from pole position and dominated the 67-lap race in consummate style as he came home 3.7 seconds ahead of local hero, defending champion Sebastian Vettel of Red Bull.
Briton Jenson Button of McLaren, who had proved the potential of his revamped car for a long spell in the race, came home third after being passed by Vettel, who ran wide and off the track, on the penultimate lap.
The race stewards announced they were investigating Vettel's passing move, a statement that left the result unconfirmed pending the result of their decision and any chosen sanction.
Finland's Kimi Raikkonen finished fourth for Lotus ahead of Japanese Kamui Kobayashi and his Sauber team-mate Mexican Sergio Perez, who came home sixth.
Seven-time champion and German hero Michael Schumacher, 43, finished seventh for Mercedes ahead of Australian Mark Webber in the second Red Bull and another German, Nico Hulkenberg, who was ninth for Force India.
Another German, Nico Rosberg, in the second Mercedes, finished 10th. It was Alonso's third win this year after his triumphs in Malaysia and at the European Grand Prix and it moved him 34 points clear of Webber in the title race with 154 points to the Australian's 120.
"That was fantastic, again," Alonso told the Ferrari team on their radio. "Tonight we make some parties on the plane!"