Republican John McCain unveiled a major surprise in the White House race Friday with his pick of first woman governor of Alaska, Sarah Palin, as his running-mate, campaign officials said. A political outsider and relative unknown on the national stage, Palin, 44, a mother of five children, emerged late Thursday as the dark horse candidate for McCain's vice-presidential nominee. The choice marks a huge political risk by McCain, and a blatant bid to win over disgruntled Hillary Clinton supporters. Palin, reportedly a former entrant in the Miss Alaska contest, could appeal to the Republican's grassroots conservative base, as she is strongly pro-life and backs the gun lobby. As a young mother she would balance out concerns over McCain's age who celebrated his 72nd birthday on Friday, and she could also be seen as a breath of fresh air, untainted by Washington politics. But unlike Clinton -- the former first lady who was defeated in the Democratic primary nominating race by Barack Obama -- Palin as a first-time governor elected in Alaska in 2006 has no national experience. The reports came as Minnesota Governor Tim Pawlenty, who had been leading in the VP tips, told a local radio station that it was “a fair assumption” he had not been picked by McCain. The news completely overshadowed Obama's historic speech to a jubiliant crowd of 84,000 fans crammed into a Denver stadium late Thursday at which he urged voters to help “restore America's promise.” Picking such a long-shot candidate could undermine McCain's accusations against Obama that he lacks the experience to be the commander in chief of a country caught up in conflicts in Iraq and Afghanistan. And Palin could find it difficult to match up against experienced senator Joseph Biden, the Democrats' vice presidential pick, who has spent his much of his 36-year career working on foreign policy. CNN reported that a private plane from Alaska landed in Dayton, Ohio on Thursday night, sparking speculation that Palin could join McCain at a midday rally in this crucial battleground state where he is set to reveal his choice. Palin is the first woman to lead Alaska and is best known for aggressively pushing for drilling in the Arctic National Wildlife Refuge, a key part of McCain's energy policy. Palin would also help McCain maintain his image as a maverick outsider: she gained popularity as a crusading rebel and whistle blower against corruption among fellow Alaskan Republicans. After appearing with his running mate here, the Republican team was to head to two other battleground states – Pennsylvania and Missouri – ahead of the Republican convention in St. Paul, Minnesota, which kicks off on Monday. Former Republican presidential hopeful Mitt Romney and independent Senator Joe Lieberman had been also top contenders for the VP spot.