NEW YORK (

TheStreet

) -- Rick Santorum has a simple strategy: Just knock.

The former Pennsylvania senator pulled off a treble Tuesday night thanks to gritty grassroots campaigning in two states Mitt Romney had won handily in 2008 and in another that had zero delegates at stake.

Rick Santorum raps on doors.

"Last night was a very good night for

the campaign, 3 states 3 wins. Help me build on that," Santorum tweeted Wednesday.

Sizable wins in Minnesota and Missouri along with a tight and shocking victory in Colorado showed the efficiency of Santorum's thinly staffed campaign (compared to Romney), which maximized doorknobs and minimized wasteful spending on air campaigning.

Granted, Santorum should still have difficulty winning the broader GOP primary race as front-runner Romney seems to have an unending mound of cash, but woe to the candidate who underestimates Santorum's commitment to shake every hand and knock on every door wherever his tennis shoes can tread.

Santorum operatives touched down in Missouri, Colorado and Minnesota immediately after Florida's Jan. 26 debate, where Romney rolled over Newt Gingrich and swept up the momentum of the race. Santorum and his campaign felt their resources would be wasted in Florida's money pit, and they knew Romney's organization in Nevada made him a virtual lock.

So they went to Missouri and Minnesota -- states that share physical borders with Iowa -- with the hope that they could pick up evangelicals and conservative-base Republicans. And they initially went to Colorado to simply cut down the 60% of votes Romney received there in 2008.

Tuesday was supposed to be the first baby-step in a long process for Santorum to begin clawing back into the race. As one

Santorum source said last week: "We're not going to try to land a knockout blow against anyone, our job is to basically make the case and make the case and make the case."

Landing a knockout blow against Romney seems impossible; even multiple victories on Super Tuesday for one of his opponents wouldn't be enough to discourage the former Massachusetts governor. But last night could have dealt the stinging jab that will have forced GOP voters in the remaining primaries to give Santorum a hard look.

Santorum's campaign quickly pivoted from Florida to snag one, maybe two quick states.

The Atlantic

reporter Molly Ball highlighted, before the Iowa caucuses

, Santorum's obsessive commitment to retail campaigning and how his hard work earned him shocking victories in the past: He got his start in politics with a victory against a seven-term incumbent congressman and four years later, at 36, rose to the U.S. Senate with a victory against the incumbent senator.

Santorum sent a crew last week to Missouri, even though the state's primary was nothing more than a beauty contest, but the campaign went there because it felt that to grab the headline would be significant enough. Again, the fight to beat Romney, the campaign thought, would be extended and any headline would be another step towards catching the front-runner.

"I think the whole purpose of being here and being strong on the ground here for this primary attests to the fact that it shows our viability as being the one that can take on Gov. Romney and beat him head-to-head," a Santorum campaign source in Missouri said last week.

Santorum's people rallied volunteers in Missouri, and they sold out dinners in Colorado. They sent a crew to Minnesota days ahead of the Nevada caucuses because they saw opportunity in the Midwestern state.

Possible victories in Missouri and Minnesota became clearer for the Santorum camp less than 24 hours before voters went to the polls, but a chance at Colorado wasn't in the cards.

A Santorum campaign source said in a Feb. 3 interview that they were "actually kind of

cautiously optimistic about Colorado."

By Monday, Santorum campaign sources were saying

Colorado could be considered a solid showing if the candidate cut into the 60% of votes Romney received there in 2008.

By Tuesday, as the Colorado caucuses opened and showed Santorum with an early lead, his campaign sensed a shift. "I actually think we can win it," one campaign source said. The returns were showing massive flips in counties that voted firmly for Romney in 2008.

Santorum and Romney were in a virtual lock about 12 minutes before Colorado GOP Chair Ryan Call announced the winner at 1 p.m. EST Wednesday, but Santorum's camp wasn't shaken: "We're pretty confident."

For the next eight minutes, nothing happened as the Colorado GOP waited to announce the final tally.

"We won Colorado! About two minutes to announcement," a Santorum campaign source in Missouri text messaged a few minutes before the official declaration. "

40%-35%. Just got the call from the party chair at 98%

of precincts in," another Santorum source text messaged a moment later.

Indeed, minutes later Colorado announced that Santorum had won by that count, which meant he had won all three races for the day. The former senator bagged the upset thanks to hard-nosed effort by his campaign staff to knock on doors and crisscross states that had been overshadowed by the electric Florida primary and the haphazardly run weekend Nevada caucuses.

How'd Santorum win? He used his knuckles.

-- Written by Joe Deaux in New York.

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