Updated at 3:10 p.m. with Cruz comments.

Sen. Ted Cruz acknowledged Wednesday that he is in a tight race and has lost momentum after new polls showed Rep. Beto O'Rourke closing in.

A Texas Lyceum poll showed a statistical dead heat, with Cruz ahead by 41 to 39, well within the margin of error of plus or minus 4.67 percentage points, which technically means that either could be ahead.

Hours later, the Quinnipiac University Poll put Cruz leading 49 to 43. A May 30 survey from the same pollsters showed Cruz ahead by 50 to 39, meaning the Democrat has cut the incumbent's lead nearly in half.

These are by far the closest snapshots of the contest in any poll taken since O'Rourke jumped into the race in early 2017. If they're accurate, a seismic political shift is underway in Texas, a state dominated by Republicans for more than two decades.

In an email to donors, the Cruz campaign conceded that momentum is on O'Rourke's side. In a brief interview at the Senate, he took the sobering polls in stride.

"There have been polls all over the place but there is no doubt that the far left is energized and angry and that is reflected in the record breaking fundraising Congressman O'Rourke is seeing, as liberals all over the country are pouring millions of dollars into his campaign," he told The Dallas Morning News. "We are taking the campaign very seriously."

Other Republicans seeking statewide office hold far more commanding leads.

Peter Brown, assistant director of the Quinnipiac poll, called the Cruz lead "slight" and "by no means overwhelming." O'Rourke, he said, "has done a good job making the race competitive."

Although Cruz's pollster publicly questioned the accuracy of the Lyceum poll, the campaign quickly blasted out a headline about the 2-point gap, with the subject line "Dead heat."

"We need your help to stem the tide of their growing momentum and we need to get the momentum back," read the Cruz fundraising email.

Gov. Greg Abbott is ahead by 16 points against former Dallas County Sheriff Lupe Valdez (47 to 31, with 22 percent undecided) among likely voters. Among registered voters, Abbott's lead jumps to 19 points, with 44 per percent saying they'll back the governor for re-election.

Lt. Gov. Dan Patrick and Attorney General Ken Paxton both hold 10-point leads over their challengers among likely voters.

But the numbers of undecided in these races were higher than for governor or Senate. In the showdown between Democrat Justin Nelson and Paxton, who has been indicted for securities fraud, 43 percent of registered voters surveyed said they didn't know who they'd vote for. Two of 5 said they didn't know whether they'd support Patrick or his Democratic challenger, Mike Collier.

Responding to the results, Collier's spokesman Scott Spiegel said he was "highly confident that this is a winnable race."

The poll also surveyed adult Texans on what they think of President Donald Trump, Abbott and Patrick's job performances. The governor received the highest grade, with 54 percent approving. But Texans are split on Trump, the poll showed, with 52 percent saying they disapprove and 44 percent saying they approve of his performance.

Cruz's pollster, Chris Wilson, has criticized the methodology used by the Lyceum poll. He argues that it has a record of including far too many non-voters to provide an accurate prediction and far too many self-identified Democrats than typically cast ballots in Texas. He asserted that when the flaws in the latest poll are taken into account, Cruz's lead is likely 10 to 12 points.

He also questioned the Quinnipiac poll, saying that its focus on registered voters rather than likely voters skews the results away from a realistic picture of midterm turnout.

"O'Rourke continues to nip at Cruz's heels, but it's a long way to go until Election Day," said Josh Blank, Lyceum poll research director. "If this race looks different than the rest, that's probably because it is because a strong Democratic challenger raising prolific sums of money and tons of earned media."

The Cruz campaign used the tight poll results released Aug. 1 to drum up donations.

Blank responded to criticisms from Cruz's camp by noting that for the first time this year, Lyceum pollsters surveyed likely and registered voters as well. In the past they have polled adult Texans, leaving the results open to criticism as a poor indicator of actual election outcomes.

"Chris Wilson is an excellent campaign pollster and he's doing what he's supposed to be doing, which is to elect his candidate to office," Blank told The News. "The only difference between Chris and the Texas Lyceum is that he has an interest in who wins the race, and how it's covered, the Texas Lyceum does not."

OK, last tweet as I feel like this horse is pretty dead now, but let's examine reported vote among whites: TC 51/BO 34--anyone know the last Dem to get over 30% with whites? (1st right answer gets WPAi moleskin). Not representative of reality #txsen #txlege pic.twitter.com/RWfCrGOrkU — Chris Wilson (@WilsonWPA) August 1, 2018

The Cruz-O'Rourke showdown is the nation's costliest Senate contest, and O'Rourke has defied expectations by blistering past the incumbent in fundraising. In the second quarter of 2018, he raised $10.4 million, compared with Cruz's $4 million. And he has raised $10 million more than Cruz overall.

O'Rourke quickly cited the poll in a fundraising solicitation.

"The momentum is on our side," he emailed potential donors. "Today's poll proves our hard work is paying off.

Cruz said his willingness to face his challenger in five debates reflects the fact that he's taking the race seriously. O'Rourke challenged the senator to six debates. He hasn't agreed to the terms the senator laid out last week for topics, dates, sites and formats, and he reiterated his preference for six.

"I don't think there is another race with a starker substantive divide between the candidates than this Texas Senate race," Cruz said, adding that for voters, "The debates will be helpful."

Independent handicappers have kept an eye on the Texas race but haven't listed Cruz as endangered. Texas hasn't elected a Democrat statewide since 1994, when Republicans led by George W. Bush swept all but one statewide contest.

Until Wednesday, the RealClearPolitics polling average of recent polls showed Cruz leading by just over 8 percentage points. In some states that would be a comfortable margin. But Texas Republicans aren't used to such close calls.

Cruz has warned his supporters in donor solicitation emails sent before the latest polls that the news has been "VERY BAD" and as recently as Tuesday, he noted that his opponent had pulled within single digits.

Cruz won his seat in 2012 with a 16-point margin. In 2014, Sen. John Cornyn won a third term by 27 points, though both faced much weaker opponents than O'Rourke. Trump edged Hillary Clinton in Texas by nine points.

"O'Rourke makes a good impression on voters, but only about half the Texas electorate has formed an opinion of him," said Brown. Sen. Cruz has a good favorability overall and is the much better known of the two men."

O'Rourke's war chest will allow him to mount an ad blitz in the fall to close that gap.

Texas Democrats were encouraged. The state party's executive director, Crystal Perkins noted in a statement that none of the GOP incumbents tops 50 percent support.

"One thing is now clear: the 2018 election is going to be close," she said. "The majority of working Texans disapprove of Donald Trump and they just aren't buying what Texas Republicans are selling.

The Lyceum poll was conducted July 9 to July 26, a 17-day window that critics called unusually long. Respondents were split 50/50 between landline and cellphone users.

Washington correspondent Rachel Cohrs contributed to this report.