Mercedes Formula One driver Lewis Hamilton of Britain drives during the Hungarian F1 Grand Prix at the Hungaroring circuit in Mogyorod, near Budapest. (Reuters Photo)
While Ferrari has slipped behind the pace in recent races, Mercedes is finally adding consistency to its undoubted speed to give Hamilton an outside shot at closing the gap on championship leader Vettel.
Hamilton, the 2008 champion, is fourth overall and has nine races left and 48 points to make up on the three-time defending champion.
But Mercedes has won three of the past five races and Hamilton has clinched three consecutive pole positions - the last three weeks ago when he drove superbly from the front to win the Hungarian GP in Budapest.
"It's been a really positive season for me," said Hamilton, who made a high-profile switch from McLaren.
"Everyone was talking me down at the beginning of the year. Some things were said about being the right or wrong decision, and that it was a mistake," he added. "The team and I have constantly proved everyone wrong, race by race."
Track temperatures hit 50 degrees Celsius (122 degrees Fahrenheit) on the Hungaroring, but conditions are often rainy in Spa, where Hamilton won three years ago. The 7.004-kilometer (4.352-mile) circuit is the longest on the calendar and it the most demanding, along with Monaco.
Because of track's vast size, different microclimates mean it can be raining on one part of the track and sunny at another. Corners such as Eau Rouge and Blanchimont push drivers and tires to the absolute limit.
"Spa is a fantastic circuit and it's so much fun to drive," Hamilton said. "We're all looking forward to the second half of the season and the opportunity to bring home some more good results."
Tires have been a factor all season, with manufacturer Pirelli under massive pressure to make them more reliable after races were marred by tires shredding too easily and even blowing up, leading to a boycott threat from drivers.
Given the incident-free Hungarian GP, rivals should now be able to focus purely on catching Vettel.
Vettel was in a similar position to Hamilton last year. He headed to Belgium trying to figure out how to make up a 42-point deficit on overall leader Fernando Alonso.
Ferrari was Red Bull's expected main rival this season, but Mercedes is now ahead in the constructors' championship, and Hamilton is only nine points behind Alonso, who slipped to third behind Kimi Raikkonen after a disappointing Hungarian GP.
"We're second in the constructors' championship, which is a massive boost," Hamilton said. "We never would have thought we'd be in such a competitive position, still within shooting distance of both championships."
Since winning the Spanish GP in front of his home fans on May 12, Alonso has managed only two podiums. In Hungary, he was fifth and he has not qualified higher than third all season, leaving him too much to do on race day.
Off the track, Alonso also landed himself a public rebuke from Ferrari after comments he made alluding to needing a better car.
Along with Alonso's current malaise, other issues behind the scenes will develop in the coming days and weeks.
Raikkonen's future with Lotus is unclear and the Finn has also been linked with a move to Ferrari.
With five second-place finishes to add to his win at the Australian GP, he must be wondering where he would be with a better car - closer than 38 points behind Vettel.
"I would have to give Kimi 10 out of 10. He's done a terrific job right from the beginning of the season and his remarkable run of 27 consecutive points finishes speaks for itself," Lotus team principal Eric Boullier said. "He is playing a big part in pushing the team forwards."
Ferrari team principal Stefano Domenicali called a meeting on Tuesday to urge his team to focus only on the races ahead, not next season.
"We have spelt it out many times before: the driver topic is definitely not a priority," Domenicali said. "If they have a winning car in their hands, then I am convinced they will know how to win with it. If we all believe, then we can do it."
What seems certain is that Raikkonen will not drive alongside Vettel next season, with the spare Red Bull seat reportedly a certainty for Toro Rosso driver Daniel Ricciardo.
Red Bull is expected to confirm in Spa that the Australian will replace Mark Webber, who is retiring from F1 at the end of the season to race sports cars for Porsche.