Sen. Ted Cruz, left, and Rep. Beto O'Rourke.
The challenge from Mr O'Rourke in Texas had threatened to derail his rise.
Cruz was backed by his 2016 presidential opponent President Donald Trump and other prominent Republicans.
In North Texas, early voting results had O'Rourke with a strong lead in Dallas County with 65.7% compared to Cruz's 33.68%.
Milner milestone in vain as Arsenal holds Liverpool
Arsenal's Emirates Stadium home had become a toxic place to be in the last days of Arsene Wenger's 22-year reign. Arsenal started the game off well, although they failed to take advantage of their early dominance.
Cruz had attempted to shame O'Rourke's language throughout the campaign, even releasing a 30-second mashup of the Democrat swearing at events while warning Texans that the lawmaker's rallies were not a "great place to bring the kids".
"My confidence is in the people of Texas", O'Rourke told reporters on Monday night, moments before staging a raucous rally with Mariachi band at the University of Texas at El Paso, mere blocks from his home. A Democrat hasn't won a Texas Senate seat since 1988, and no one from the party has captured any statewide office since 1994, the nation's longest political losing streak.
Trump and Cruz were bitter 2016 rivals, but the president visited Houston late last month to solidify the senator's win. It's the time for action. "They're filled with rage and hatred for the president". He set fundraising records and made Cruz work for the victory, but Cruz ultimately pulled out a three-point victory.
O'Rourke, whose campaign raised a record-setting $60 million, was a long-shot to defeat Cruz, a Republican, in the historically red state of Texas, despite finding widespread support nationwide in one of the most closely-watched races of the election.