The first official debate between Massachusetts Republican Sen. Scott Brown and his Democratic challenger Elizabeth Warren began Thursday with a discussion about Warren's Native American heritage.

Brown devoted his opening remarks to accuse Warren, a Harvard Law School professor who says she is part Cherokee Indian, of using her background to give her an advantage when competing for jobs throughout her career.

"The professor said she is a Native American, a person of color, and you can see she's not," Brown said in the first moments of the debate, echoing an attack line that has dogged Warren throughout much of the race this year.

Warren, who appeared to be caught off guard, was forced to use her opening remarks to respond, and she denied that she had taken advantage of affirmative action programs when seeking jobs.

"I never used it," Warren said, adding later: "I didn't get an advantage because of my background."

The debate moderator quickly moved the conversation to other topics. The candidates went on to debate tax rates, abortion (both candidates support protecting access), education and laws that enforce "equal pay for equal work" for men and women in the workplace.

The Massachusetts Senate race is considered one of the highest-profile contests in the country. Brown, a moderate Republican, won the seat two years ago in a special election after Democrat Edward Kennedy, who had held the seat since 1962, died in 2009. Warren, who helped start President Barack Obama's Consumer Financial Protection Bureau before launching her bid for the Senate, has a national following among liberals because of her work on consumer issues.

The candidates will hold three more debates before Election Day.