Sunday's feat was the Spaniard's second win of the season, in five races, and the 32nd win of his career – a triumph that endorsed his challenge for a third drivers' title on an afternoon of Spanish supremacy at the Circuit de Catalunya.
Driving with great aplomb, Alonso delivered a beautifully judged performance to win a tactical contest dominated by tyre-wear management, finishing 9.338 seconds ahead of second placed Finn Kimi Raikkonen of Lotus.
Alonso said to the 95 000-strong crowd: "What a fantastic feeling, you feel the support from everybody, we wanted to do well here in front of our fans, so many people supporting Ferrari."
Alonso's Ferrari teammate Brazilian Felipe Massa started from ninth, but finished third ahead of defending triple world champion Sebastian Vettel and his Red Bull teammate Mark Webber.
Rosberg loses out
Alonso's win bucked a trend at the Catalan circuit, where 18 of the previous 22 events were won by the driver who started from pole position. This time the pole-sitting German Nico Rosberg of Mercedes finished sixth ahead of Paul Di Resta of Force India.
Jenson Button finished a measured eighth for McLaren ahead of his teammate Sergio Perez with Australian Daniel Ricciardo of Toro Rosso completing the top 10 finishers.
Lewis Hamilton, who started from second alongside Rosberg, struggled hom 12th on a disappointing day for him and Mercedes.
Alonso picked up a Spanish flag from a steward on his slowing down lap and ignited national celebrations as he completed his tour of the crowded circuit.
In the drivers' championship, Alonso jumped to third with 72 points behind leader Vettel on 89 and Raikkonen on 85. – AFP