When moderator Bret Baier asked who would not pledge not to run as an independent, only Trump raised his hand.
Donald Trump was met with boos on more than one occasion during Thursday night's debate - but he insists he had harder questions than his rivals.
In particular, he accused moderator Megyn Kelly of giving him tougher questions than other candidates.
After the debate he told reporters: "I thought their questions to me were much tougher than to other people, and I respect that, but I really enjoyed the evening.
Read: Donald Trump Calls Rosie O'Donnell a 'Fat Pig' During Debate, She Responds
"The questions to me were far tougher, and that I supposedly - according to what everyone is telling me, and the call-ins and everything, I won. But the questions to me were not nice. I didn't think they were appropriate. And I thought Megyn behaved very badly, personally."
He also took his fight to social media after the debate.
Wow, @megynkelly really bombed tonight. People are going wild on twitter! Funny to watch.
— Donald J. Trump (@realDonaldTrump) August 7, 2015
I really enjoyed the debate tonight even though the @FoxNews trio, especially @megynkelly, was not very good or professional!
— Donald J. Trump (@realDonaldTrump) August 7, 2015
It came after she quizzed him over comments he had made about women, namely calling them "fat pigs" or "slobs."
"Only Rosie O'Donnell," Trump quipped - which was met with laughter.
But the audience didn't always seem impressed with his answers. When moderator Bret Baier asked the 10 candidates who would not pledge not to run as an independent, only Trump raised his hand.
The crowd started to boo.
"I want to win as a Republican, I want to run as the Republican nominee," Trump said. "I will not make the pledge at this time."
Critics say a third party candidate would possibly give Democrats the edge in a race.
The billionaire presidential hopeful added that he could not necessarily pledge support for whomever wins the Republican battle.
“I cannot say I have to respect the person who wins," he said. "I make the pledge if I win the nomination. I have a lot of leverage.”
Read: Jeb Bush's Reportedly Told Donor: Donald Trump is a Buffoon and a Clown
Rand Paul then took a swipe at Trump.
"This is what's wrong," he said. "He buys and sells politicans of all stripes!"
But Trump brushed off the criticism. As the audience booed him at one point, he quipped: “The audience doesn’t like me."
Watch Below: Jeb Bush Reportedly Calls GOP Rival Donald Trump a Buffoon and a Clown
