(CNN) -- A boiling primary battle in Texas headed to a runoff early Wednesday as two Republicans running for U.S. Senate failed to reach the 50% threshold to clinch the GOP nomination.
Though Lt. Gov. David Dewhurst led the crowded field of candidates, he narrowly failed to cross the 50% mark required to secure the nomination and avoid a July 31 runoff.
Dewhurst's challenger in the runoff will be tea party favorite Ted Cruz, a former solicitor general with strong support from national groups and high-profile conservative leaders.
With 99.6% of precincts counted, Dewhurst held 48% of the vote to 30% for Cruz.
Other contenders in Tuesday's primary included former Dallas Mayor Tom Leppert and ESPN Broadcaster Craig James. Neither candidate will forge ahead to compete in the runoff.
The Texas race is particularly important because the balance of power in the U.S. Senate could shift in 2012. It is also another test in the staying power and influence of tea party groups and their political strategy to focus more on congressional races than on the presidential campaign.
The race, held to replace retiring Sen. Kay Bailey Hutchison, has seen a Texas-sized level of spending, as well. According to Federal Election Commission reports, more than $31.6 million had been dumped in the GOP primary as of May 9, with more than half coming from Dewhurst's team.
While Cruz's campaign has spent more than $4 million, the underdog has been boosted by a surge of outside spending. The fiscal conservative organization Club for Growth has spent more than $2 million, and the tea party oriented FreedomWorks has also been heavy on the ground in get-out-the-vote efforts on behalf of Cruz.
Members of the Tea Party Express, a leading arm of the grass-roots movement, have traversed the state by bus in support of Cruz. Adding to his rising star power, the former solicitor general landed endorsements from former GOP presidential candidate Rick Santorum and tea party stalwart Sarah Palin, two big voices in the conservative movement.
Dewhurst, meanwhile, touts his support from 2008 presidential candidate and former Arkansas Gov. Mike Huckabee.
Texas Gov. Rick Perry has also been vocal for his No. 2. In a recent commercial, Perry urged voters to turn out for Dewhurst, insisting he was the true conservative in the race.
Given that Perry and Dewhurst have worked together for almost a decade, some political observers characterize the race as a possible referendum on Perry, the state's longest-serving governor in history.
But Perry brushed off the idea on Friday, telling CNN Chief National Correspondent John King that while national conservatives may be making noise in the race against Dewhurst, the local movement will stand for the lieutenant governor.
"There's, you know, people who come from out of state and make their endorsements known," Perry said. "But Texas conservatives are lining up behind David Dewhurst."
Dewhurst opponents criticize the candidate as being part of the Republican establishment and having too many years in government under his belt. Before becoming lieutenant governor, Dewhurst served as Texas Land Commissioner in the late '90s.
Hitting back, Dewhurst points to his private sector experience as the co-founder of Falcon Seaboard, an energy company based in Houston. He also boasts his role in pushing for socially conservative legislation in the state, including a recent bill that requires women to see a sonogram and go through a 24-hour waiting period before having an abortion.
Dewhurst has attacked Cruz, who is of Cuban descent, as a supporter of amnesty and a member of the Hispanic Leadership Fund and the Hispanic Alliance for Prosperity Institute. Cruz has also been on the defense over criticism that he works for a firm representing a Chinese company being sued for patent violations.
The candidate has repeatedly shot down both claims, arguing he has long been an opponent of illegal immigration and saying he is not the lead lawyer in the patent lawsuit.
The Hispanic Leadership Fund also fired back against Dewhurst's latest ad, saying Cruz has never had any position with the group and faulted the ad as dishonest.
"The Hispanic Leadership Fund support using free market and limited government principles to strengthen border security, restore a functional legal immigration system, and promote patriotic assimilation. If David Dewhurst wants to deceitfully lump us in with leftist organizations that actually do promote amnesty, then all he is accomplishing is demonstrating to Texas voters how intellectually shallow he is," Mario H. Lopez, the organization's president, said in a statement.
On the Democratic side, former state Rep. Paul Sadler and political operative Sean Hubbard are competing for their party's nomination.
Texas has not elected a Democrat to the Senate in more than two decades.
Political handicappers Stuart Rothenberg and Charlie Cook both rate the open seat as safe for Republicans.