Steve Mitchell, president of Mitchell Research & Communications, said Romney was winning over conservative voters.
"Romney's lead seems to have solidified after real volatilty over the past two weeks. Romney has made big inroads with conservatives over the past 10 days … Romney had to persuade fiscal and social conservatives that he was more conservative than they thought he was," Mitchell said in a statement. "He also had to persuade them that Santorum was not as conservative as Santorum said he was. Romney seems to be accomplishing both those tasks."
Santorum's double-digit lead among self-identified Tea Party supporters has been wiped out, and his lead among evangelicals has been halved, according to the poll.
Respondents also named Romney the victor of Wednesday's debate, with a third of voters giving him the nod. Only 13 percent of respondents said Santorum won the debate, while Ron Paul earned 10 percent and Newt Gingrich got 9 percent.
"Romney was the clear winner in the debate last night," said John Garst, president of Rosetta Stone Communications, in a statement.
Romney surrogate and former presidential candidate Tim Pawlenty predicted Friday morning that his candidate would win the Wolverine State.
"The momentum in Michigan is on Mitt's side; if you saw the polls a week or two [ago], Rick was up substantially — now Gov. Romney has clawed back to be tied or maybe even slightly in the lead," Pawlenty said on Fox News.