Barack Obama last night made history by becoming the first black US presidential candidate and in doing so declared that the 2008 election was "our chance to keep the American promise alive".

Barack Obama last night made history by becoming the first black US presidential candidate and in doing so declared that the 2008 election was "our chance to keep the American promise alive".

Addressing 80,000 ecstatic Democratic supporters in the vast Denver Broncos stadium, the 47-year-old first term senator from Illinois brought the audience to its feet when he echoed the famous "I have a dream" speech made by Martin Luther King 45 years ago to the day.

Obama stressed how it was the promise of America which had inspired people from every corner of the country to gather to hear the civil rights champion in 1963 on the steps of Washington's Lincoln Memorial.

Adopting an evangelical tone himself, he declared: "America, we cannot turn back. Not with so much work to be done. We cannot walk alone. At this moment, in this election, we must pledge once more to march into the future."

Answering the Republican charge that he was all celebrity and no substance, as well as the high-flown rhetoric Obama spent much of his 45-minute speech going through policy subject by policy subject to show how he would implement change in America, insisting that he would cut taxes for the less well-off and small businesses, create millions of more jobs at home, make good quality education available for more people and provide universal healthcare. He also pledged to green America by investing in alternative energy so that within 10 years it could be weaned off its dependence on Saudi oil.

He declared America had reached a "defining moment when our nation is at war, our economy is in turmoil and the American promise has been threatened once more", insisting: "America, we are better than these last eight years. We are a better country than this."

To a cheering flag-waving audience, he insisted: "On November 4th, we must stand up and say: 'Eight is enough,'"

With Obama running neck and neck in the polls with John McCain, his Republican rival, he seemed to find a new aggression and pressed relentlessly with his theme that a McCain presidency would represent nothing more than four more years of the policies of the deeply unpopular President George W Bush, noting how his Republican rival had voted with the current President "90% of the time". He joked: "I don't know about you but I'm not ready to take a 10% chance on change."

In arguably his most passionate moment, the Democratic candidate said: "Tonight, I say to the people of America, to Democrats and Republicans and independents across this great land - enough!"

Responding to Republican charges that Obama was not patriotic enough, the Democratic candidate praised the US military, noting, however, that patriotism should not be used as a political tool against your opponent. He said of American troops: "They have not served a red America or a blue America, they have served the United States of America." He added: "So I've got news for you, John McCain - we all put our country first."

While the acceptance speech was the first in the open-air since John F Kennedy's in 1960 at the Los Angeles Coliseum, Obama's real audience was the millions of Americans who watched it on TV at home. Last night will be his biggest audience until he meets McCain in late September for the first of three live television debates.

The atmosphere in the Mile High stadium was one of exuberance and colour with music from Stevie Wonder and Sheryl Crow ahead of the keynote speech. Vendors sold Obama regalia from the usual caps, badges and T-shirts to Obama dolls.

Cameras constantly flashed around the stadium as illuminated signs flickered with the words "change", "America" and "Obama" at key points. After Obama's speech was over, fireworks lit the Denver skyline.

Later, the McCain camp dismissed Obama's passionate address, saying: "Tonight, Americans witnessed a misleading speech that was so fundamentally at odds with the meagre record of Barack Obama. The fact remains: Barack Obama is still not ready to be president."

Today, McCain is expected to name his running mate at a rally in Dayton, Ohio.

Speculation has fallen heavily on Tim Pawlenty, the Governor of Minnesota, who has cancelled all scheduled appearances for the next two days.

ENDS