ST. PAUL — Stevie Wonder and Chaka Khan had the crowd partying like it was 1999 all over again at a tribute concert to Prince Thursday night, a show fans and his family hoped would provide closure after his death nearly six months ago.

Khan brought Wonder onstage at Xcel Energy Center in St. Paul to duet on Prince’s “I Feel for You,” a 1984 hit for Khan. Wonder, wearing a suit and purple shirt, got the sold-out audience cheering with his signature harmonica riffs before the two performed Prince’s hit “1999,” with the crowd clapping and dancing along.

Just before show time, a concert publicist announced that singer Christina Aguilera canceled her scheduled appearance as she fights a “vocal illness.” Singer Jessie J replaced Aguilera in the lineup.

A representative for Aguilera said she “has been advised by her doctors not to perform due to a vocal illness she has been trying to shake all week.”

Pop star John Mayer bowed out of the concert earlier, citing a “change of schedule.” Singer Anita Baker canceled her appearance just before the event, but a publicist for the show did not know the reason.

On the outdoor plaza before the concert, fans wearing purple shirts, scarves and the occasional raspberry beret milled about and some danced. St. Paul Mayor Chris Coleman read a proclamation declaring Thursday Prince Day in Minnesota’s capital. President Barack Obama delivered a taped message as the concert opened.

Sharie Tonsager, 46, who grew up in suburban Rosemount, looked forward to hearing the music of Prince — a star she never got to see perform in person.

“He was just original. He never cared what the media said. He just did what he did and loved what he did,” said Tonsager, who was sporting purple-tinted hair.

Prince’s younger sister, Tyka Nelson, described the concert as a public memorial to Prince, who died in April at his Paisley Park recording complex.