"It's quite nicely poised. Vettel pretty much looked on the way to his fourth world championship this year but now with Hamilton's win in Hungary it's suddenly up for grabs between the two," Foster said.
Twelve months ago, Ferrari was providing the resistance, but Foster doesn't see that happening this year.
"They have lost quite a lot of ground with the front runners and I can't see them making that up. With the massive rules changes next year, unless you're definitely in the title hunt most teams are going to switch their focus to 2014 much sooner than usual," Foster said.
"It's still too early but you have to say it's between Hamilton and Vettel, I would have thought."
Hamilton currently lies fourth in the standings, 48 points behind championship leader Vettel and will be hoping for a repeat run of 2010 when he took the checkered flag for his old team McLaren.
"I wonder whether Mercedes has turned the corner?" Foster asks.
"You can't tell off the back of one race, but Hamilton was just untouchable. If they are very strong in Spa as well then you have to say that Hamilton has got every chance to catch Vettel in the championship."