Republican presidential hopeful Mitt Romney has been declared the clear winner of Wednesday's first campaign debate as President Barack Obama stopped short of offensive attacks against his challenger.

Some 67 per cent of those surveyed by CNN in a "flash poll" after the debate declared Romney the winner. Obama's re-election prospects on Intrade, an online prediction market, also fell from 74 per cent to 66 per cent.

The 90-minute debate in Denver, Colorado saw Romney able to keep the focus on jobs and the sorry state of the US economy and Obama forced to defend his record.

Romney himself had earlier portrayed the debates as a possible key turning point in the election and analysts had described it in recent days as a make-or-break moment for Romney, who trails Obama not only in national opinion surveys, but in the handful of key states that will determine the election's outcome.

Commentators from both sides of the political spectrum pointed to Romney as the winner immediately following the event, and a flash poll of television viewers by broadcaster CNN showed a whopping 67 per cent thought Romney had won.

Romney, his wife Ann and their family lingered on the stage afterwards, waving to the crowd and savouring the moment. The Obamas, who are celebrating their 20th wedding anniversary, on the other hand made a quick exit.

Even Obama deputy campaign manager Stephanie Cutter acknowledged, "I think that Mitt Romney, yes, he absolutely wins the preparation. And he wins the style points."

Others were harsher in their assessment, with one liberal observer on broadcaster MSNBC even exclaiming, "Where was the president tonight?"

Conservative commentators were ecstatic. Jonah Goldberg of the National Review wrote that he had not expected Romney to perform as well as he did, adding: "Romney simply dominated and deflated Obama."

Obama fails to shine

The evening was full of dry statistical exchanges and Obama failed to even raise recent campaign controversies, like a video of a Romney fundraiser that showed him disparaging 47 per cent of Americans as addicted to the government dole.

Other familiar Obama campaign jabs against Romney were also absent from the discussion, including allegations he outsourced jobs during his time at Bain Capital and questions about why Romney does not release more tax returns.

But with the two more presidential debates and a vice presidential debate scheduled in quick succession in the final weeks before the November 6 election, Obama could yet return to putting a negative twist on his attacks against Romney.

And while Romney may have won the immediate commentary war, it remains to be seen whether he has turned the voters' tide to his advantage.

A nationwide poll of likely voters released on Tuesday ahead of the debate showed Obama's lead over Romney slipping to 3 percentage points.

The latest NBC News/Wall Street Journal poll said 49 per cent of the people polled would vote for Obama, while 46 per cent said they would choose Romney. The 3-point difference is within the poll's margin of error, according to the pollsters.

The final two presidential debates are October 16 and 22. Vice President Joe Biden will debate Republican vice presidential candidate Paul Ryan on October 11.