Former U.S. senator Rick Santorum grabbed a big lead over front-runner Mitt Romney in the non-binding Republican U.S. presidential primary in Missouri on Tuesday with about 27 percent of the votes counted.

Santorum had about 54 percent of the vote while Romney - who has won three of the first five nominating contests - was in second with 26 percent, according to the Missouri secretary of state's website.

Missouri is one of three states holding Republican presidential nominating contests on Tuesday, with Minnesota and Colorado holding caucuses. They are the latest contests in the state-by-state battle for the Republican nomination to face President Barack Obama, a Democrat, in the November 6 U.S. election.

If the lead holds it would be the second victory for Santorum, the former senator from Pennsylvania who narrowly beat Romney to win Iowa's caucuses on January 3.

The Missouri primary is considered a beauty contest because the candidates do not win delegates who will take part in the August Republican convention where the party's presidential nominee will officially be chosen. Missouri Republicans will select convention delegates in caucuses on March 17 in the state's two-step process.

Newt Gingrich, who until now had been seen as the closest challenger to front-runner Romney, was not on the ballot in Missouri, allowing Santorum the chance to consolidate conservative voters as he campaigned as the best conservative alternative to the more moderate Romney.

(Reporting by Deborah Charles; Editing by Will Dunham)