GREENVILLE, S.C. — Mitt Romney’s loafers were still damp from standing under the pouring rain to give a stump speech Friday morning at the muddy Harmon Tree Farm. By the time he reached Greenville for his final rally capping the most trying week of his presidential campaign, he looked exhausted.

Yet as soon as Romney grabbed the microphone at a 9 p.m. rally here Friday night, he seemed to transform into a different candidate. Suddenly, Romney came alive. He was fiery and seemed to speak from the heart, however rehearsed he may have been. He told funny new jokes and delivered tough new lines about President Obama.

And his overflow crowd of more than 400 at a Greenville banquet hall ate it up, reacting wildly throughout.

Romney is not a candidate used to being interrupted by cheers, but on this night he was.

“We need Mitt! We need Mitt! We need Mitt!” they chanted.

“You know what?” he replied. “You’re gonna get me.”

“You guys in Greenville,” Romney added, “this is the best audience I’ve been to in a long time.”

Or ever.

It is difficult to recall a campaign event this past year where the former Massachusetts governor has made such an electric connection with his audience or where the crowd has been as pumped up as here. To be sure, Romney had some reinforcements in the form of two of the Republican Party’s star governors — South Carolina’s Nikki Haley and Virginia’s Robert McDonnell — who introduced him, as well as Romney’s wife, Ann. McDonnell recognized from the stage dozens of people in the crowd who had come from Virginia.

Still, it was Romney whom voters in the crowd said they marveled at. The man in person, some said in interviews after the rally, was nothing like the stiff, scripted and humorless politician they have come to know through 16 candidates’ debates.

“He was much more animated and humorous and much, much more likeable than what I’ve seen on TV. I came in undecided. We came down to see if he’d give us anything more than he had, and he did. I’m going to vote for him now,” said Janet Johnson, 70, who drove with her husband more than an hour from her home in Salem to help decide whether to vote for him or former House speaker Newt Gingrich.

This week, Romney bore witness to the resurgence of Gingrich, who shot up in the polls after two strong debate performances and probably dashed any hopes Romney had of locking up the nomination in South Carolina. Romney’s performance Friday night may have came too late — and before too small an audience — to make up for the double-digit lead he has squandered here.

But the Greenville rally illustrated how Romney’s competitive instincts can kick in, and it may signal a shift in his campaign style — from tentative to scrappy. The front-runner may lose to Gingrich here on Saturday. If he does, the race is on. And if Friday night was any indication, Romney is ready to fight for it.

“I happen to believe that I’m the only guy in this race who can beat Barack Obama,” Romney told the Greenville crowd, drawing loud applause. It’s a judgment about electability sometimes put forth by his surrogates, but rarely until now by Romney himself.

“I think you have to have someone who’s had experience in the private sector, who knows how the economy works, who can bring that experience to post up against Barack Obama, a different background, different experiences, can stand up to him and say, ‘You know what? Your stimulus did not work, Mr. Obama,’” Romney said.

“Your policies have hurt the enterprise of America,” he continued. “You made it harder for the economy to recover and I know because I’ve been in that economy. Your policies with regard to trade, energy, health care, taxation — they’re wrong. I know they’re wrong because I’ve been in the private sector and I’ve seen what impact they’ve had.”

The Greenville rally concluded a difficult week for Romney, which began at a debate Monday where he stammered over questions about his reluctance to release his federal income tax returns. The next morning, Romney drew a meager crowd of fewer than 100 at what his campaign billed as a “grass-roots rally” in Florence. Huge swaths of the civic center floor were bare.

After he sized up the crowd, Romney offered excuses: “You guys are great to get up, what time is it here? Nine o’clock in the morning in Florence. Gosh, this is a workday, right? Oh yeah! I appreciate you spending some time with me.”

Later, in Florence, Romney told reporters that he would release his returns in April and estimated his rate was about 15 percent, setting off a series of stories and even more questions that would hang over his candidacy all week.

Then he was stripped of his victory in the Iowa caucuses, struggled through some portions of another debate and tried to find his footing after a rival, Texas Gov. Rick Perry, abruptly dropped out and endorsed Gingrich.

Romney’s confidence never disappeared, but it certainly was softened at that tree farm in Gilbert on Friday morning. He breaks up his stump speeches by reading lyrics from his favorite patriotic hymns, including “America the Beautiful,” but he added a new twist to what had become a practiced joke of his.

“O beautiful for spacious skies, for amber waves of grain,” Romney said. “When I was in Iowa, I joked that the corn counted as an amber wave of grain. That may account for my slim, uh, defeat there. I used to say that accounted for an eight-point win, but I had to change my rhetoric in the last couple of days.”

Ten hours later, after a rally in North Charleston and chartering a plane to Greenville with Haley and McDonnell, Romney exhorted his crowd to vote — “In some places you can vote multiple times. . .but not here,” he joked.

“This is a race about choosing someone who can beat President Obama and can lead America back to strength,” Romney said. “I will do that with your help tomorrow. Let’s get the job done.”

At that, Romney tossed his microphone back to Ann and dove into the crowd, shaking hands and exchanging pleasantries with all those people who were chanting his name.