(Screenshot of CNN)

The three wins were projected to put Romney near the half-way mark of the 1,144 delegates needed to lock up the GOP nomination. Nevertheless, Santorum has pledged to go all the way to the convention. 

"We won 'em all," Romney shouted at his victory speech.

Only Wisconsin was competitive, a state where Santorum led in polls just a few weeks ago. 

With 96 percent of the precincts reporting in Wisconsin, Romney led Santorum 42.5 percent to 37.7 percent. 

Santorum had hoped to pull away a critical upset over Romney in Wisconsin, but TV networks projected the former Massachusetts governor would easy win over Santorum, Newt Gingrich and Ron Paul. 

With 100 percent of Maryland precincts reporting, Romney took a commanding win over Santorum, 49 percent to 28.9 percent. With all precincts reporting in DC, Romney won with 70.2 percent of the tally. 

A number of recent high-profile endorsements, including ones from Florida's Jeb Bush and Sen. Marco Rubio, Rep. Paul Ryan, and former president George H.W. Bush, helped Romney claim the three big wins.