US Republican presidential nominee Donald Trump's supporters are turning out in droves - in online polls, at least.

Of the almost 1.5 million votes on Time magazine's website, 54 per cent judged Mr Trump the winner of the US presidential debate on Monday (Sept 26) night (Tuesday morning, Singapore time), against Democratic candidate Hillary Clinton's 46 per cent.

He enjoyed a similar margin on left-leaning news site Slate.

Mr Trump also won the approval of 66 per cent of respondents on news channel CNBC's website, and 72 per cent of respondents on infotainment site Heavy.com.

Similarly, 76 per cent of Breitbart News readers thought he had won the debate. Breitbart is a heavily conservative website whose former head, Mr Stephen Bannon, is chief executive of Mr Trump's campaign.

But in a twist that shows that Mr Trump has captured a radical segment of the right wing while alienating mainstream conservatives, only 50 per cent of Fox News readers felt he had proved his mettle in the presidential debate.

Another 15 per cent thought that there was no clear winner, while 35 per cent bit the bullet and called it a win for Mrs Clinton.

Online sentiment should, of course, be taken with a bushel of salt.

Slate admitted as much when it called its online poll "totally unscientific".

The Asian markets seemed to view the debate outcome as a win for Mrs Clinton, with shares rebounding late Tuesday morning alongside a surge in the Mexican peso.

A CNN poll found that 62 per cent of respondents felt that Mrs Clinton had won the debate against 27 per cent for Mr Trump, and most mainstream political analysts thought Mrs Clinton did better in the debate.