Fox News Channel anchors and debate moderators (from left) Chris Wallace, Megyn Kelly and Bret Baier begin the debate among Republican presidential candidates in Des Moines, Iowa, Thursday. REUTERS

GOP front-runner Donald Trump may have evaded Fox News anchor Megyn Kelly's fiery line of questioning, but he left rivals to take the hits Thursday at the Fox News-Google debate in Des Moines, Iowa. Trump was invited to the prime-time debate, but opted not to attend due to what he said was unfair treatment from Kelly at the first GOP debate in August.

And the "Kelly File" host was quick to push back at the GOP candidates' responses Thursday night. Among the candidates grilled by Kelly were Texas Sen. Ted Cruz and Florida Sen. Marco Rubio, who rank second and third in the polls behind Trump, respectively. Kelly produced a trove of video clips of Rubio's previous statements on immigration, which revealed inconsistencies in his policies. "Have you already proven that you lied on amnesty?" Kelly said.

Appearing caught off balance, Rubio reddened and blinked several times before pivoting to his foreign policy on addressing the Islamic State terror group.

Rubio was not the only one to face pointed questions from Kelly on immigration. Employing another video montage, she asked Cruz whether he too supported amnesty at some point. The footage showed Cruz supporting an immigration bill that would have allowed undocumented immigrants to receive permanent status but not citizenship. "Was that all an act? It was pretty convincing," Kelly said.

Earlier in the night, Kelly asked Cruz why he was willing to attack Trump after months of holding his tongue.

"The divide between you and Mr. Trump has turned into one of the biggest stories in the country," Kelly said. "And for six months that — your campaign, during this campaign, you praised Mr. Trump as somebody who you thought was an effective voice against the Washington cartel. You said you were glad that he was running as a Republican. But when he started to criticize you, your message changed, and you suddenly started to portray him as the voice of the Washington cartel, and suggested he would do the Democrats' bidding. Which is it?"

Cruz insisted that he has not insulted Trump — despite kicking off the debate moments before with an impression of the businessman. "Let me say I'm a maniac and everyone on this stage is stupid, fat, and ugly," he said. "And Ben, you're a terrible surgeon. Now that we've gotten the Donald Trump portion out of the way..."

Rubio and Cruz were joined on the main stage by retired neurosurgeon Dr. Ben Carson, former Florida Gov. Jeb Bush, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich and Kentucky Sen. Rand Paul.

Four candidates were relegated to the earlier debate for their low- tanding in the polls. Former Hewlett-Packard CEO Carly Fiorina, former Arkansas Gov. Mike Huckabee, former Pennsylvania Sen. Rick Santorum and former Virginia Gov. Jim Gilmore were invited to the so-called undercard debate at 7 p.m. EST.

The prime-time showdown aired at 9 p.m. Thursday EST on Fox News Channel.