Donald Trump took center-stage Thursday night in Houston as the irrefutable front-runner in the final Republican debate before Super Tuesday. Flanking the billionaire, Sens. Ted Cruz and Marco Rubio sought to make clear that the quest for the Republican nomination is a three-man race, not a one-man show. Here are the most memorable moments of the night:

1. Rubio engages Trump
Fielding a question on immigration, Rubio in his response went after Trump for hiring illegal immigrants and paying $1 million after a suit was filed. Rubio pointed to some of the businessman's past stances on immigration, remarking that many of Trump's positions are new.

"Donald, you've hired a significant number of people from other countries to take jobs that Americans could have filled," Rubio said, charging that Trump has hired more than a thousand immigrants to fill domestic jobs.

Trump said he hired immigrants for part-time jobs during hot seasons in Florida that most people didn't want to work.

"You're the only person on this stage that's ever been fined for hiring people to work on your projects illegally," Rubio responded.

Trump charged that he's the only person on stage who's hired anyone at all.

After a tense exchange, Rubio concluded, "He hired workers from Poland and he had to pay a million dollars or so in a judgment. That's a fact."

While Trump maintained Rubio was wrong, Cruz later jumped in to say Trump was found guilty as part of a conspiracy for hiring people illegally.

2. Cruz has no friends in the Senate
Trump, who scored his first two congressional endorsements this week, hammered Cruz for lacking Senate support.

"I got along with everybody," he told the Texas senator. "You get along with nobody. You don't have one Republican — you don't have one Republican senator and you work with them every day in your life, although you skipped a lot of time — these are minor details. But you don't have one Republican senator backing you. Not one…You should be ashamed of yourself."

Cruz's response? Trump does get along with everybody — especially Democrats. "You know, I actually think Donald is right. He is promising that if he's elected he will go and cut deals with Washington, and he's right," Cruz said. "He has given hundreds of thousands of dollars to Democrats."

3. Rubio takes Trump to school
Moments after Rubio and Trump's immigration squabble, Rubio invoked another lawsuit Trump has been involved in — this time with Trump University.

Trump touted his deal-making prowess as he talked about how the U.S. is losing jobs to Mexico and China. "You don't know anything about it because you're a lousy businessman," Rubio said. "I don't know anything about bankrupting companies. I don't know anything about starting a fake university."

People borrow $36,000 in loans to attend a "fake school," Rubio said. "And you know what they got? They got to take a picture with a cutout of Donald Trump. That's what they got for $36,000."

4. Selling watches
In another skirmish, after Trump mentioned Rubio's financial history, the Florida senator suggested the brash billionaire wouldn't even be on stage had it not been for the riches he inherited.

"Here's a guy who buys a house for $179,000 and sells to it a lobbyist who's probably here for $380,000 and then legislation is passed," Trump said. "You tell me — this guy!"

"If he hadn't inherited $200 million, you know where Donald Trump would be right now? Selling watches in Manhattan," Rubio shot back.

Trump, of course, dismissed Rubio's claim and played up his business skills, saying he flipped $1 million into $10 billion. "No, no no, that is so wrong," Trump responded. "I took $1 million and I turned it into $10 billion.

5. Limit on lies
Trump supporters rarely challenge Trump on the veracity of his often controversial remarks. But Rubio isn't a Trump supporter and accused him of lying about the lawsuit in Poland.

"Yeah, yeah, yeah. That was 38 years ago," Trump said.

"Oh, he lied 38 years ago," Rubio said sarcastically. "I guess there's a statute of limitation on lies."