Updated

Republican Pat Toomey's campaign says it has no plans to change course as the polls suddenly tighten in the Pennsylvania Senate race, a contest that once looked like a lock for the GOP.

Ahead of the candidates' debate Wednesday evening in Philadelphia, a new poll from The Muhlenberg College/Allentown Morning Call showed Democratic Rep. Joe Sestak overtaking Toomey, who was leading by as much as 10 percentage points just last week.

Though Sestak has a history of coming from behind with late-in-the-season surges, Toomey's campaign dismissed the new polling and pledged to keep the focus on the economy in the 13 days remaining.

"We're going to continue doing what we're doing, spreading our message for creating jobs," spokeswoman Nachama Soloveichik told FoxNews.com.

Voters can anticipate an escalating round of campaign trail accusations as Sestak challenges expectations in the race, which Toomey for months has dominated. Toomey is the conservative candidate whose popularity forced Sen. Arlen Specter -- facing a crushing defeat in the GOP primary -- to cross over to the Democratic Party. Specter ended up losing his seat after Sestak built a late surge to beat him in the Democrats' primary.

More On This...

With the Democratic congressman looking to repeat that strategy, both candidates are keeping packed agendas in their final get-out-the-vote push.

Toomey is planning a rally outside Philadelphia on Friday with former New York Mayor Rudy Giuliani. Starting next week, the Republican nominee will be flying around Pennsylvania, attending local rallies and meeting voters.

Sestak is also planning a rally Friday after the candidates' second debate in Pittsburgh. His Sierra Club supporters are planning a day of door-knocking this Saturday, while the Brotherhood of Carpenters & Joiners are planning a pro-Sestak canvass in southwest Philadelphia the same day. Sestak got some high-level help from President Obama at a recent rally in Philadelphia.

In this hard-to-predict state, Republican strategists have started to express concern about Toomey's standing. The Specter seat is a key part of the GOP's strategy and a virtual must-win if they want a shot at seizing the chamber from the Democrats.

The party reportedly pulled money out of the Florida Senate race, where GOP candidate Marco Rubio enjoys a sizeable lead, and pumped more money into Pennsylvania. The new poll in the race showed Sestak leading 44-41 percent among likely voters; the margin of error was 5 percentage points.

But Soloveichik expressed confidence in Toomey's chances.

"The polls are all over the place, with most of them showing a good sized lead for Pat Toomey," she told Fox News. "But the bottom line for Pennsylvania voters is a clear choice between more of the same reckless Washington spending and high unemployment with Joe Sestak, or a change in direction toward fiscal discipline and job growth with Pat Toomey."

Toomey has hammered Sestak for supporting policies like the health care package and Wall Street bailouts, but Sestak took to the airwaves with a quirky new ad to counter that message.

The campaign's new ad shows the Sestak family walking their dog, while the candidate himself picks up the dog's droppings. The droppings apparently are a metaphor for the financial "mess" left behind by Republicans.

"It made me sick to bail out the banks, but I had to clean up the mess left behind by these guys," Sestak said in the ad. "Now Pat Toomey is attacking me for cleaning up his mess."

Toomey's campaign called the ad "desperate" and "laughable."