Texas Lt. Gov. Dewhurst and tea party-backed Ted Cruz are headed to a runoff for the GOP nomination to the U.S. Senate.
Both are vying to fill the seat vacated by retiring Sen. Kay Bailey Hutchison.
At 9:30 p.m., with 4 percent of precincts reporting, Dewhurst had 45 percent of the vote to Cruz's 32 percent. Former Dallas Mayor Tom Leppert conceded his race for the seat at 8:30 p.m. with only 14 percent of the vote.
"I felt like we got in it for the right reasons. I think we've conducted the campaign in the right manner and I think we conducted ourselves in ways that we can be proud of," Leppert said. "I got to tell you, when you do something like this you're humbled by the number of folks that rallied around you and I've just been very fortunate and I'm appreciative."
Ex-NFL running back and ESPN announcer Craig James has tallied 4 percent of the vote. See the latest returns for this race here.
Dewhurst said he helped make the Lone Star state one of the country's most-conservative, serving as lieutenant governor since 2003. But Cruz, an attorney and former state solicitor general, said the tea party wave that began in 2010 is still going strong.
The runoff will be held on July 31.
NBC 5's Kevin Cokely contributed to this report.