WASHINGTON -- America's talk show diva Oprah Winfrey will join Barack Obama to watch as he is crowned the Democratic Party's presidential candidate, her office confirmed Thursday.

Obama will give his acceptance speech before a crowd of about 75,000 people at the Invesco field football stadium in Denver in a break with tradition which is likely to prove a spectacular climax to the four-day party convention.

"She will be there," a spokeswoman for her publicist told AFP, without giving further details.

A close friend, Gayle King, also told the television program Entertainment Tonight that the 54-year-old high priestess would join Obama for the final night, but would not address the crowds.

Winfrey is one of the nation's most influential women, and her endorsement of Obama may give him a significant edge in November's presidential elections among women and black voters in key election states.

Her legendary book club on her afternoon television chat show has turned unknown authors into best sellers.

The show is estimated to attract up to 10 million viewers daily and she earned $260 million in the year 2007, according to Forbes Magazine.

Now Winfrey hopes her support could sway the loyal legions of female Hillary Clinton supporters who were disappointed by the former first lady's defeat by Obama in the party's primaries.

Forbes magazine recently described Oprah as the most powerful celebrity in the United States, ahead of golf star Tiger Woods and Hollywood actress Angelina Jolie.

After throwing her support behind Obama late last year, Winfrey accompanied him for the Iowa, New Hampshire and South Carolina primaries. She has also organized a fund-raising benefit at her home in Santa Barbara, California.

But the Illinois senator, who has sparked "Obama-mania" with tens of thousands flocking to his rallies, is walking a delicate tightrope in handling the star-studded support he has already attracted.

His Republican rival John McCain earlier this month released a scathing video comparing Obama to troubled popular culture divas Paris Hilton and Britney Spears, and mocking his global celebrity.