HOUSTON — Front-running Joe Biden stood out the most in Thursday’s snoozer of a Democratic debate — but for all the wrong reasons as he rambled through responses laden with non sequiturs about record players and Danish philosopher Søren Kierkegaard.

“Play the radio. Make sure the television — excuse me, make sure you have the record player on at night, the phone … make sure that kids hear words, a kid coming from a very poor school, a very poor background will hear 4 million words fewer spoken by the time they get there,” the former vice president, 76, babbled at one point.

It wasn’t clear if he was about to go from record player back to phonograph, or if he was about to make a point about cellphones.

The labyrinthine answer — mercifully cut short by a moderator — came in response to a straightforward question about whether Biden felt an obligation to make amends for prior generations’ school segregation.

Biden hardly got his train of thought back on track by his closing statement, name-dropping 19th-century thinker Kierkegaard when asked to address his greatest professional failure.

He also, at one point, managed to make a pretzel out of a question about whether American troops being pulled out of Iraq too early allowed ISIS to gain a foothold — launching into an answer about air bases in Afghanistan.

“Here’s the point, the point is that it’s a counter-terrorism strategy. We can prevent the United States from being the victim of terror coming out of Afghanistan by providing air bases and insisting the Pakistani provide bases for us to airlift from and move against what we know,” opined Biden.

Biden’s tongue-tied musings brought guilty levity — if little else — to the marathon three-hour proceedings.

Hopes that a pared-down field taking the debate stage for just one night in Houston — and pitting poll heavyweights like Biden and Massachusetts Sen. Elizabeth Warren against each other for the first time this cycle — would spark a fire went unfulfilled, as any early fireworks quickly fizzled.

Biden, Warren and fellow top contender Vermont Sen. Bernie Sanders largely played it safe, clinging to their respective oft-repeated talking points, and the seven trailing candidates did little to capitalize.

Reheated attacks on President Trump, as in earlier debates, often drowned out discourse among the 10 White House hopefuls.

Most of the highlights to be found came in the first third of the droning affair.

Former Housing and Urban Development Secretary Julián Castro, the last of the 10 participants to qualify for Thursday’s debate, feebly tried to swing for the fences, sniping at bigger targets like Biden and South Bend, Ind., Mayor Pete Buttigieg.

“Are you forgetting what you said just two minutes ago?” Castro asked Biden after catching the former vice president in a contradiction on his health care proposal. “I am fulfilling the legacy of Barack Obama and you are not.”

Buttigieg interjected with a plea for party unity despite their more nuanced ideological differences.

“This is why presidential debates are becoming unwatchable,” said Buttigieg, the youngest among the field at 37. “This reminds everybody of what they cannot stand about Washington: scoring points against each other, poking at each other.”

Castro swatted down the “kumbaya” sentiment: “That’s called the Democratic primary. … That’s called an election.”

Former Texas Rep. Beto O’Rourke — playing with home-state advantage, and riding the emotional wave of last month’s mass shooting at a Walmart in his town of El Paso — made crystal-clear his intended plan for assault weapons if elected.

“Hell, yes, we’re going to take your AR-15, your AK-47,” thundered O’Rourke, who received several positive call-outs from his opponents for his poise in comforting the reeling El Paso community. “We’re not going to allow it to be used against our fellow Americans anymore.”

Outsider candidate Andrew Yang ran out of gas even earlier, peaking in his opening statement in which he tried to entice voters with the promise of $120,000 gifts to 10 families as a teaser for his “freedom dividend” proposal.

But Yang, at least, had a highlight-reel moment, unlike virtually invisible participants like Minnesota Sen. Amy Klobuchar and California Sen. Kamala Harris, who seemed to gain a head of steam in the first round of debates by pummeling Biden, only to abandon the strategy for breathless broadsides at Trump.

Among those participants in the first two rounds absent from viewers’ screens Thursday night, casualties of the Democratic National Committee’s polling and donor restrictions, were Mayor Bill de Blasio, Hawaii Rep. Tulsi Gabbard and quirky internet darling Marianne Williamson.

Those who missed the cut — hitting 2 percent in at least four DNC-approved polls and registering at least 130,000 unique donors — for Thursday can still punch a ticket for next month’s fourth round in Ohio if they meet the thresholds by Oct. 1.

Additional reporting by Nolan Hicks, Ebony Bowden and Tamar Lapin