Former US president Donald Trump turned in a better performance than President Joe Biden during the first of presidential debates, a shift from 2020 when debate watchers saw the 81-year-old Democrat as outperforming his Republican rival.

During Thursday's feisty debate that lasted roughly 90 minutes, President Biden and 78-year-old Trump sparred over the economy, immigration, foreign policy, abortion and national security. Both the leaders called each other a liar and the worst president in the history of the US.

Sixty-seven per cent to 33 per cent of the registered debate watchers said that Trump turned in a better performance, according to a CNN flash poll conducted by SSRS.

CNN was the host of the first of the three presidential debates held in Atlanta.

Before the debate, the same voters said, 55 per cent to 45 per cent, that they expected Trump to perform better than Biden.

The poll’s results reflect opinions of the debate only among those voters who tuned in and are not representative of the views of the full voting public – in their demographics, political preferences or the level of attention they pay to politics.

Debate watchers in the poll were 5 points likelier to be Republican-aligned than Democratic-aligned, making for an audience that was slightly more Republican-leaning than all registered voters nationally.

But the results are a shift from 2020 when Biden was seen by debate watchers as outperforming Trump in their presidential debates, CNN reported.

A 57 per cent majority of debate watchers Thursday night said they have no real confidence in Biden’s ability to lead the country, and 44 per cent that they have no real confidence in Trump’s ability to do so.

Those numbers are effectively unchanged from the poll taken before the debate, in which 55 per cent of those voters said they had no confidence in Biden and 47 per cent that they lacked confidence in Trump.

Neither candidate scores highly on this metric, but while just 36 per cent of debate watchers now say they have a lot of confidence in Trump’s ability to lead the country, only 14 per cent say the same of Biden, the report said.

The CNN poll was conducted by text message with 565 registered US voters who said they watched the debate Thursday, and the poll findings are representative of the views of debate watchers only, CNN emphasised.

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