It's not often that a late replacement turns out to be an unexpected bonus. But so it proves when Alyson Williams stands in for Glenn Jones. Introduced by headliner Jean Carne as "the first female singer on Def Jam Records", Williams launches into the heady R&B of "Sleep Talk", one of three Top 40 hits she scored in the UK in 1989.
Even without the hats she used to wear on Top of the Pops, she towers over the audience of soul cognoscenti, who have travelled from as far away as Holland, and regales us with stories of Jazzie B producing "I Need Your Lovin'". The laid-back, sensuous, sinuous, Soul II Soul-like groove works a treat here, as does the shimmering "Can't Have My Man". She even gets away with covering Simply Red's "Holding Back the Years", and closes with the signature ballad "Just Call My Name", a quiet storm favourite on urban radio in the US.
Then Shirley Jones of the Jones Girls takes to the stage. She and her two sisters were late arrivals at Kenny Gamble and Leon Huff's Philadelphia International party, but became cult favourites in the UK with singles including "Nights Over Egypt", covered by Incognito in 1995.
Starting with the title track from the 1980 album At Peace With Woman and seguing into the cute "Dance Turned Into a Romance", she takes us back to the days when Philly Soul turned into disco. The highlight of her sizzling set is the slow jam "Do You Get Enough Love?", originally intended for the O'Jays, which topped the US R&B charts in 1986 for Jones as a solo artist.
With the other two providing backing vocals for whoever is centre stage, this most engaging evening has none of the diva moments associated with the R&B stars of the Nineties and Noughties. Mind you, "Free Love", Carne's infectious opener, shows that, with her five-octave range, she could teach Mariah Carey or Beyonc a thing or two. One minute, the grande dame of Philadelphia International is growling like Eartha Kitt, the next she's hitting soprano heights.
She follows the classy "Mystic Stranger" with her perennial disco anthem "Was That All It Was?" and reclaims the seminal symphonic soul of "Don't Let It Go To Your Head" from the clutches of Britain's Brand New Heavies. "Closer Than Close", with Carne's voice dipping then soaring, is that rare thing, a slow song that works as a finale.
Sisters in song and soul, Williams, Jones and Carne would each be worth the price of admission on their own. On the same bill, they are simply unbeatable.
Ends tonight (0870 060 3777; www.jazzcafe.co.uk)