AP

ABC News' Michael Falcone and Shushannah Walshe report:

The closing days of the Illinois primary have brought an onslaught of television and radio advertising from Mitt Romney and his super PAC allies - most of it aimed squarely at squashing Rick Santorum's hopes of pulling off an upset in next Tuesday's primary.

On Friday the campaign released a new TV commercial calling Santorum's economic know-how into question. "He's never run a business or a state," the ad's narrator says, calling the former Pennsylvania senator "another economic lightweight."

To help get that ad and others on the air, Romney's campaign chipped in an additional $100,000 on Thursday on top of their already $900,000-plus ad buy in the state, according to GOP media trackers.

Even more firepower is coming from the pro-Romney super PAC, Restore Our Future, which has purchased roughly $2.5 million worth of airtime ahead of the primary

The spending is a sign of how high the stakes are for the Romney campaign in Illinois coming on the heels of the former Massachusetts governor's losses on Tuesday in Alabama and Mississippi. It's also an indicator of how close the race is shaping up to be.

Romney is spending both time and money in the state, campaigning there on Friday and again beginning Saturday night through Tuesday's primary.

Compared to Romney's all-in approach, Santorum's campaign and the pro-Santorum super PAC, the Red, White and Blue Fund, have merely dipped their toe into the political waters of the Land of Lincoln.

Santorum and the super PAC are spending just over half-a-million dollars in the state - the campaign has invested about $200,000 and the super PAC kicked in roughly $310,000 more.

The Red, White and Blue Fund released a new ad on Thursday titled "Meet," which attacks Romney.

"Meet the real Mitt Romney," the narrator says. "Supported the Wall Street bailout putting America trillions in debt. Raised job-killing taxes and fees by over 700 million, leaving Massachusetts over 1 billion in debt. His healthcare takeover was the blueprint for Obamacare. Mitt Romney. More debt and taxes, less jobs. More of the same."

The ad calls Santorum a "leader with a bold plan for the middle class."

Santorum is facing similar spending imbalances in two states that will hold nominating contests after Illinois. In Louisiana, which holds its primary on March 24, Romney and his allies are outspending Santorum and his supporters two-to-one. And in Wisconsin, with its contest more than two weeks away, Romney and the pro-Romney super PAC have a whopping 28-to-one spending head start on Santorum.