When Hamilton came in to change tyres for the first time on lap 12, he rejoined right behind Romain Grosjean and got embroiled in a fight with the Frenchman. It delayed Hamilton just enough for Alonso to rejoin right on the Mercedes racer's tail when he made his tyre stop. Both drivers cleared Grosjean before Hamilton ran slightly wide at La Source hairpin, allowing Alonso to nip ahead on the run down the hill to Eau Rouge.
The second Mercedes of Nico Rosberg finished fourth. The German came under pressure from Webber in the closing stages, but was able to keep clear enough of the Australian to ensure he couldn't deploy the Drag Reduction System to attack on the straights.
Jenson Button qualified and finished sixth in one of his most competition races of the season. He ran long into the race before making his first pit stop to open up the possibility of using a one-stop strategy. Indeed, he briefly led the grand prix after Vettel had come in for fresh rubber on lap 14.
But Button felt he should have remained out on the first set of tyres for a couple of extra laps. It left him in a strategical no-man's land, and when his front tyres began to wear heavily McLaren decided to deploy a two-stop strategy. It ruled out any prospect of a surprise podium finish for the 2009 world champion, but kept him in a solid points-scoring position after a more encouraging race.
Felipe Massa was hampered by a handling imbalance in the opening stages of the race, but recovered to overtake one-stopping Grosjean for seventh position in the closing laps.
Paul di Resta underlined his talent by qualifying a brilliant fifth in his Force India, but in the race he bogged down off the start line and fell back to seventh position. It was the start of a frustrating afternoon that ended with him getting punted into a spin by the out-of-shape Williams of Pastor Maldonado.
Kimi Räikkönen was another retirement. Having spent most of the race with brake dust belching from his front left wheel, his race came to an end when his over-worn brakes finally failed as he battled with Felipe Massa.
Vettel's win has put him 46 points clear of Alonso in the points standings, with Hamilton a further 12 points behind.
Belgian Grand Prix, 25 August 2013
1 Sebastian Vettel (Red Bull)
2 Fernando Alonso (Ferrari)
3 Lewis Hamilton (Mercedes)
4 Nico Rosberg (Mercedes)
5 Mark Webber (Red Bull)
6 Jenson Button (McLaren)
7 Felipe Massa (Ferrari)
8 Romain Grosjean (Lotus)
9 Adrian Sutil (Force India)
10 Daniel Ricciardo (Toro Rosso)