With eight races left, Vettel heads to the Italian GP in two weeks' time with 197 points — 46 ahead of Fernando Alonso and 58 clear of Lewis Hamilton, who leapfrogged Kimi Raikkonen into third overall after the Finn retired from the race.
Alonso finished the race 16.8 seconds behind Vettel in second spot and Hamilton nearly 30 seconds back in third.
"The car was better than we expected going into the race, which I really enjoyed," Vettel said. "Fortunately there was no rain, so no need for any critical calls to be made, and a comfortable afternoon for us."
Talk heading into Spa was of Hamilton — winner of the previous GP in Hungary last month — emerging as Vettel's biggest threat.
The Mercedes driver put himself in a great position to pressure Vettel, starting ahead on the front row after securing his fourth consecutive pole position.
But Vettel took precisely 31 seconds to silence any doubters.
That was how long it took him to overtake Hamilton on the first lap, and he was never in trouble afterward.
As he crossed the line, the 26-year-old German pumped his right fist and then wagged his finger aloft — reminding everyone who really is No. 1 and admonishing those who may have questioned that.
"For sure it's a positive message today," he said. "Looking forward to Monza now."
It was Vettel's fifth win of the season, the second from three GPs, and 31st of his career.
"When the car works well you don't want the race to stop," he said. "The car was just a pleasure to drive."
Alonso drove brilliantly from ninth on the grid to give Ferrari a timely boost and a first podium since the British GP.
Mercedes driver Nico Rosberg finished fourth ahead of Vettel's Red Bull teammate Mark Webber.
Hamilton become the first Briton since Damon Hill in 1995 to achieve four straight poles and sat on the front row for the seventh consecutive race.
Vettel has not secured a pole since winning the Canadian GP in June.
But it made little difference.
"Once I passed him (Hamilton) I had incredible pace and took control until the end," Vettel said.
Although Hamilton made a good start and held his line at the first turn into La Source turn, Vettel moved into the slipstream of his Mercedes and surged past him down the uphill Kemmel straight.
"Sebastian just caught me massively," Hamilton said. "I just had to watch him glide by."
Alonso looked like he was on a mission as he carved through the field, passing last year's Spa winner Jenson Button and Rosberg to move into third.
"The car had the speed," Alonso said. "The weekend was good for us ... We felt more competitive."
After earning a one-race ban for reckless driving at last year's race, where his dangerous driving sent three drivers off the track at the first turn, Frenchman Romain Grosjean seemed desperate to avoid even the slightest contact. He ended up on the receiving end when Sergio Perez got a drive through penalty for forcing him off track.
Hamilton was the first of the contenders to pit for new tires, followed by Alonso, but Vettel stayed out three laps longer.
Halfway through the 44-lap circuit — the longest in F1 at 7.004 kilometres (4.352 miles) and the most difficult along with Monaco — Vettel already led by eight seconds.
Raikkonen, meanwhile, had to abandon on lap 26 with smoke coming from his front right brake, ending his run of scoring points in 27 consecutive races.
Shortly after, Pastor Maldonado crashed into the side of Paul di Resta.
Di Resta, the British driver who had high hopes after qualifying fifth, looked disconsolate as he trudged off, helmet in his hand and his race over.
Before the race, protesters from the environmental group Greenpeace staged a brief demonstration against race sponsor Shell's plans to drill in the Arctic.
Two paragliders flew over the circuit, trailing a banner, and others then climbed onto the grandstand roof to unfurl a 20-meter long banner that read "ARCTIC OIL? SHELL NO!"
After pitting wits, Hamilton and Vettel then combined to ambush former F1 driver David Coulthard on the race podium, spraying him with their Champagne bottles.
"I've only rented the suit for the day," joked a drenched Coulthard. "I have to give it back."Suggest a correction