By Corrie MacLaggan
AUSTIN, Texas (Reuters) - Voters began heading to the polls on Tuesday in Texas, where Tea Party movement favorite Ted Cruz is hoping to upset Lieutenant Governor David Dewhurst in a fiercely competitive Republican primary runoff for an open U.S. Senate seat.
Insurgent Republicans across the country want Cruz to become the latest to topple an establishment Republican, similar to victories in Senate primaries this year in Indiana and Nebraska.
A poll released over the weekend by the Democratic survey group Public Policy Polling showed Cruz ahead by 10 percentage points, 52 percent to 42 percent, an increase from a five-point lead two weeks earlier.
The automatic telephone survey of likely Republican runoff voters, which had a margin of error of plus or minus 3.8 percentage points, said that Cruz had a 75-22 advantage with voters who consider themselves members of the Tea Party.
The Tea Party emerged amid the economic recession of 2008 and 2009 and seeks deep federal government spending cuts and low taxes. It took its name from the 18th-century Boston tea party protest over taxation by the British king.
"Runoffs are unpredictable and it still seems possible that Dewhurst could win on Tuesday, but for now it looks like all the momentum since the primary has gone in Ted Cruz's direction," Tom Jensen of Public Policy Polling wrote in a blog post.
If elected to the seat being vacated by Republican Senator Kay Bailey Hutchison, Cruz, whose father is from Cuba, would be the first Hispanic U.S. Senator from Texas.
Dewhurst, 66, who presides over the state senate, has put $19 million of his own money into the race, his campaign said. He also has the backing of top Texas Republicans including Governor Rick Perry. Dewhurst is a former state land commissioner who has served in the U.S. Air Force and with the Central Intelligence Agency.
He has dismissed Cruz as not having enough experience and running a campaign that depends on "Washington insiders."
In Cruz's corner are national conservative stars such as former Alaska Governor Sarah Palin and national groups such as the Club for Growth and FreedomWorks that have funneled money and volunteers to his campaign.
Cruz, 41, a Houston lawyer and former state solicitor general, says that Dewhurst is not conservative enough and has compromised too much with Democrats in the state senate.
In the final days of the race, the candidates have crisscrossed the state to talk to voters while their attack ads played on TV.
On Friday, Cruz held a rally in the Houston area featuring Palin and Tea Party favorite U.S. Senator Jim DeMint of South Carolina.
On Monday, Dewhurst campaigned at an Austin Chick-fil-A - the fast food chain at the center of a firestorm since its president made statements against gay marriage - before holding campaign events with Perry and former Dallas Mayor Tom Leppert.
Leppert, who has endorsed Dewhurst, finished third in the May primary election, when Dewhurst was the top vote-getter in a crowded field but did not secure the 50 percent plus one vote he needed to avoid a runoff with Cruz.
Two Democrats are also in a U.S. Senate primary runoff on Tuesday, but Texas has not elected a Democrat to statewide office since 1994.
(Reporting By Corrie MacLaggan; Editing by Philip Barbara)