After trailing Rick Santorum by as much as 10 percentage points, Romney battled back to within a point behind the former U.S. senator from Pennsylvania, RealClearPolitics.com's average of polls indicated.
Romney turned in a good performance in last week's debate in Arizona, blunting some of the momentum Santorum had going into the gabfest and this week's primaries in Michigan and Arizona and caucuses in Washington.
Romney also picked up several key endorsements, including a nod from Michigan Gov. Rick Snyder.
After the debate in Mesa, Romney campaign adviser Stuart Stevens guaranteed the former Massachusetts governor would claim the Michigan primary Tuesday, CNN said.
"We are going to win Michigan," Stevens said. "We are going to win Michigan."
However, another Romney adviser said the candidate didn't have to post a win in Michigan to prove himself.
"Mitt Romney has connections to three states," Eric Fehrnstrom told MSNBC.com "Four years ago we won all three of three of those states [Michigan, Utah and Massachusetts]. Is any one of them a must-win for Mitt Romney? No."
"I think the must-do for any candidate running for president is achieving the 1,145 delegates," Fehrnstrom added. "That's what's going to secure the nomination, and it's a long process, and as of right now we have a nearly three to one lead over our closest rival in terms of delegates."
Still, Michigan has become another key test for Romney as he fights to take the battleground state once led by his father. A loss to Santorum -- after dropping Colorado, Minnesota and Missouri -- would again highlight the difficulty Romney has rallying Republicans and cramp his campaign heading into Super Tuesday on March 6.
After Santorum jumped to front-runner status and led Romney in the state, several national polls indicated his lead shrank enough to move the state into the "toss up" category, MarketWatch.com said.
"Next Tuesday's election is pivotal for Mitt Romney," GOP consultant Mike Dennehy told The Washington Post. "Michigan is really the battleground for the future of the nomination."
The well-financed Romney campaign banks on a good, overall performance to reinforce the candidate's status as a front-runner and electability, analysts told the Post.
"It's no longer possible to focus all your energies on a single state and mobilize a small core group to show well in that state," GOP consultant Fred Malek told the Post. "Rather, it requires a broader appeal, and I predict Romney wins big over next two weeks."
Other, candidates, lacking the resources financial and otherwise, will need to be more judicious, analysts said.
Santorum, for example has been campaigning in Michigan, Arizona and Washington as well as Super Tuesday states. His advisers said Santorum's schedule reflects of strong poll numbers and fundraising efforts.
"We're running a national campaign, "Santorum spokesman Hogan Gidley said, adding, "[In] general, states where the Republican electorate is more moderate are less good for us, and states where the electorate is more conservative are good for us."
Former House Speaker Newt Gingrich, who has repeatedly said he's in the hunt until the Republican National Convention in Tampa, Fla., in August, has largely skipped the contests this week to concentrate on Super Tuesday contests in Ohio, Oklahoma, Tennessee and his home state of Georgia.
U.S. Rep Ron Paul of Texas also has been spending time in Michigan ahead of the primary.
Michigan doesn't register voters by parties but primary-goers must request the ballot for the party primary in which they will vote.
Michigan Republicans will get 42 delegates based on the results within the state's 14 congressional districts and another 14 at-large. However, only 30 will be able to vote at the national convention because Michigan violated GOP rules by advancing its primary.