Downs, who sang "I'm Afraid This Must Be Love" for her talent routine, bested Miss Louisiana Jennifer Dupont, who performed a jazz dance for hers.
Miss North Carolina Kristin Elrod was second runner-up, followed by Miss Arkansas Lacy Fleming and Miss California Veena Goel.
Downs, who wants to be a pediatrician, will take up the cause of childhood cancer prevention during her reign as Miss America. In fact, she already has: She helped persuade the state of Alabama to offer a "Curing Childhood Cancer" car tag, the purchase of which will help fund cancer research.
"I would love to be the Miss America that really brings this organization back into the fabric of popular culture, makes this part of Americana again," she said after winning.
Fifty-two women — including, for the first time ever, a contestant from the U.S. Virgin Islands — competed for the crown in a two-hour show producers hoped would turn the tide on declining TV ratings.
Taking a page from reality TV, Miss America producers spiced up the prime-time special by enlisting "The Bachelor" host Chris Harrison, crooner Clay Aiken and some new production touches in a bid to keep people watching.
The telecast marked the 50th year since Sept. 11, 1954, when Lee Meriwether was crowned Miss America 1955 during the first Miss America pageant to be televised.
This year's pageant retained the same basic elements, but with plenty of updates, including the Miss America Quiz, an eight-question pop quiz on U.S. history, U.S. government and current events given to the five finalists.
The talent competition, which once showcased 10 of the contestants, was trimmed to two, and the traditional "parade of states" introduction of the contestants was reworked to eliminate some of the tedium.
In a nod to successful reality shows like "Last Comic Standing" and "American Idol," Downs and Dupont squared off in a head-to-head talent showdown near the end of the telecast to help the seven-judge panel decide who got to make the tearful runway walk in Boardwalk Hall.
Downs will get more than that, though: She earned a $50,000 college scholarship, a modicum of overnight celebrity and a yearlong reign that can net up to $200,000 in appearance fees.
Citing hour-to-hour Nielsen ratings that traditionally ebb during the talent competition, pageant producers axed the often-amateurish singing, dancing or baton-twirling acts that had been a part of Miss America since 1938.
The swimsuit contest was briefer, too, in a sense. Showing more skin than ever, the contestants competed in racy two-piece swimsuits provided to Miss America under a two-year sponsorship deal with maker Speedo.
Downs succeeds Miss America 2004 Ericka Dunlap, 22, an aspiring attorney from Orlando, Fla., who spent her year advocating the celebration of diversity.