Donald Trump came ready to take on any opponent on the crowded stage in the second televised Republican candidate 2016 presidential debate.
The billionaire businessman and brash front-runner was firing off in all directions from the start as his rivals tried to puncture his high-flying candidacy.
Mr Trump has so far proven untouchable despite a series of remarks that would have undone a more traditional candidate.
A highlight came when former Hewlett-Packard chief executive Carly Fiorina, the only woman in the Republican field, drew big applause when asked about Mr Trump's earlier denigration of her appearance, about which he later backtracked.
"I think women all over this country heard very clearly what Mr Trump said," she said as Mr Trump's face became red.
Mr Trump retorted: "She's got a beautiful face, and she's a beautiful woman."
Trump has been unpredictable, as he was in the first moments of the debate, declaring that Rand Paul should not even be on the stage.
Standing centre stage, Mr Trump declared that he had a "phenomenal temperament" and a record in business that would help him on the world stage.
The unlikely rise and surprising staying power of Mr Trump, who remains a long-shot for the White House and has never held public office, has sidelined all other candidates.
His climb to the top of the field has unnerved Republican leaders who fear the former reality TV star's tough talk, especially about women and Hispanic immigrants, is damaging the party's brand.
They worry he is harming its chances of winning back the White House after President Barack Obama's eight-year tenure is over.
Mr Trump has so far been immune to criticism for his lack of specific policy proposals, his incendiary rhetoric and his uneven support of conservative principles.
The first question of the debate went to Ms Fiorina, who called Mr Trump a "wonderful entertainer" but said all the candidates' characters would be revealed over time and under pressure.
Mr Paul, the only candidate to directly challenge Mr Trump in the first debate, said he is worried about having Mr Trump in control of the US nuclear arsenal.
Ms Fiorina was the newest addition to the main debate after a stand-out performance in an under-card event last month.
The race has seen another unlikely surge, as soft-spoken retired neurosurgeon Ben Carson has leapt into second place, according to polls.
Four candidates lagging behind in national polls did not qualify for the main event and were relegated to an earlier debate.
They were Louisiana governor Bobby Jindal, South Carolina senator Lindsey Graham, former Pennsylvania senator Rick Santorum and former New York governor George Pataki.