DENVER (AP) — Republican John McCain shook up the presidential race with his surprise choice of little-known Alaska Gov. Sarah Palin as his running mate on Friday. Democrat Barack Obama, entering a crucial stage of the campaign fresh off his historic nominating convention, began a tour of battleground states.

Obama left the convention city of Denver as the first black man to be nominated for president by a major political party. The 47-year-old Illinois senator won over the party faithful — even some die-hard backers of Sen. Hillary Rodham Clinton — but the broader electorate awaits.

McCain, who turned 72 on Friday, worked to grab the spotlight with his selection of Palin, 44, the first woman to be a Republican vice presidential nominee.

‘‘I have found the right partner to help me stand up to those who value their privileges over their responsibilities, who put power over principle, and put their interests before your needs,’’ McCain said at a raucous rally in the swing state of Ohio.

The Republican presidential nominee-to-be stunned some party officials by choosing the self-styled hockey mom and political reformer, who has been governor of her state for less than two years, over several more prominent prospects including Minnesota Gov. Tim Pawlenty, former Massachusetts Gov. Mitt Romney and former Pennsylvania Gov. Tom Ridge.

‘‘It turns out that the women of America aren’t finished yet,’’ she said, praising Clinton, ‘‘and we can shatter that glass ceiling once and for all.’’

Seizing on themes Obama has made trademarks of his candidacy, she added, ‘‘If you want change in Washington, if you hope for a better America, we’re asking for your vote.’’

Democrats quickly pounced on Palin as inexperienced, noting that Republicans have argued Obama is not ready to be president.

‘‘John McCain has made his candidacy about a single argument — experience — and Sarah Palin doesn’t have it,’’ Rep. Chris Van Hollen, D-Md., said in a statement.

McCain and his newly minted running mate were to make a midday appearance at a rally in swing-state Ohio and continue to rallies in Pennsylvania and Missouri in the run-up to the Republican National Convention, which starts Monday in St. Paul, Minn.

Polls show a tight race between Obama and McCain, with some two months before the election and three high-stakes debates. Neither contender can allow the other to jump out to a big post-convention lead.

Obama was flying to Pittsburgh, where he and running mate Joe Biden will kick off a bus tour of Pennsylvania, Ohio and Michigan. Their goal is to maintain the buzz of a convention that culminated Thursday night with Obama addressing an energetic, flag-waving crowd of 84,000 packed into Denver’s pro football stadium.

‘‘Change happens because the American people demand it — because they rise up and insist on new ideas and new leadership, a new politics for a new time,’’ Obama told the adoring crowd at Invesco Field. ‘‘America, this is one of those moments.’’

In the jam-packed football stadium, Obama promised an end to eight years of ‘‘broken politics in Washington and the failed policies of George W. Bush’’ and argued that McCain ‘‘doesn’t get it.’’

He pledged to cut taxes for nearly all working-class families, end the war in Iraq and break America’s dependence on Mideast oil within a decade. Portraying a McCain administration as a continuation of the current Bush White House, Obama said, ‘‘On Nov. 4, we must stand up and say: ’Eight is enough.’’’

Obama accepted his party’s nomination on the 45th anniversary of Martin Luther King Jr.’s ‘‘I Have a Dream’’ speech. He alluded to the historic parallel — and its promise — toward the end of his 44-minute speech.

‘‘What the people heard … people of every creed and color, from every walk of life — is that in America, our destiny is inextricably linked. That together, our dreams can be one,’’ Obama said.

In Ohio Friday, McCain and Palin both noted that he was choosing her as his vice presidential running mate the week of the 88th anniversary of women’s suffrage.

Palin has a strong anti-abortion record, and her selection was praised warmly by social conservatives whose support McCain needs to prevail in the campaign for the White House.

‘‘It’s an absolutely brilliant choice,’’ said Mathew Staver, dean of Liberty University School of Law. ‘‘This will absolutely energize McCain’s campaign and energize conservatives.’’

Palin has five children, the youngest born in April with Down syndrome.