Christina Aguilera performs in a cleavage-revealing top at Etta James' funeral

Christina Aguilera stole the show at Etta James's funeral with a performance of 'At Last' in a cleavage-revealing outfit.

The 31-year-old looked fantastic in a fitted black suit and gold cross chain as she belted out a moving rendition of the song at the blues legend's memorial service at a church in Gardena, just outside of Los Angeles.

Christine, who received rave reviews on Twitter, told Etta's friends, family and fans that she has included At Last in every concert she's performed as a tribute to her musical inspiration.

Etta triumphed against all odds to break down cultural and musical barriers in a style that was unfailingly honest.

The Reverend Al Sharpton, a civil rights activist, eulogised James in a rousing speech, describing her remarkable rise from poverty and pain to become a woman whose music became an enduring anthem for weddings and commercials.

Perhaps most famously, President Barack Obama and the first lady shared their first inaugural ball dance to a version of the song sung by Beyonce, who portrayed James in the film Cadillac Records.

Mr Sharpton opened his remarks by reading a statement from the president.

"Etta will be remembered for her legendary voice and her contributions to our nation's musical heritage," Mr Obama's statement read.

The Grammy-winning singer died January 20 after battling leukaemia and other ailments, including dementia.

She had retreated from public life in recent years, but her legacy was on display as mourners of all ages and races converged on the City of Refuge church in Gardena, south of central Los Angeles.

Stevie Wonder also performed three songs, including Shelter In the Rain and a harmonica solo. James' rose-draped coffin was on display, surrounded by wreaths and floral arrangements and pictures of the singer.

Mr Sharpton, who met James when he was an up-and-coming preacher, credited her with helping break down racial barriers through her music.

"She was able to get us on the same rhythms and humming the same ballads and understanding each other's melodies way before we could even use the same hotels," Mr Sharpton said, referring to the era when racial segregation was the law in many US states.

He said James' fame and influence would have been unthinkable to a woman with James' background - growing up in a broken home during segregation and at times battling her own demons.

"The genius of Etta James is she flipped the script," Mr Sharpton said, alluding to her struggles with addiction, which she eventually overcame.

"She waited until she turned her pain into power," he said, adding that it turned her story away from being a tragic one into one of triumph.

"You beat 'em Etta," Mr Sharpton said in concluding his eulogy. "At last. At last. At last!"

The assembly roared to their feet, and would again stand to applaud performances by Wonder and Aguilera, who filled the sanctuary with their voices.

"Out of all the singers that I've ever heard, she was the one that cut right to my soul and spoke to me," Aguilera said before her performance.

Throughout the service, a portrait of James as a woman who beat the odds in pursuit of her dreams repeatedly emerged.

James won four Grammy Awards, including a lifetime achievement honour, and was inducted into the Rock and Roll Hall of Fame in 1993. In her decades-long career, she became revered for her passionate, soulful singing voice.

James is survived by her husband of 42 years, Artis Mills, and two sons, Donto and Sametto James.

"Mom, I love you," Donto James said during brief remarks. "When I get to the gates, can you please be there for me?"