Following her debut goalscoring feat in a 4-0 win at Rayo Vallecano last week, Asisat Oshoala's fine first-half finish in the 17th minute strengthened Llius Cortes side's title bid at the Mini Estadi.
However, Raquel equalised in the 59th minute before Stephaine van der Gragt's own goal gifted the visitors a lead two minutes later.
While the title hopefuls were still pushing for a comeback, Morocco's Hajri teed up Maria Bonsegundo to score what turned out the winner in the 67th minute, thus putting the match out of reach.
Oshoala completed her brace after pulling one back for Cortes' side - her third goal in two games, but her effort could not prevent them from suffering their first defeat of the season.
The shock defeat now leaves Barcelona six points behind leaders Atletico Madrid, who pipped rivals Madrid 2-0 at the Estadio Municipal Nuevo Matapinonera on Wednesday.
For Hajri's Sporting de Huelva, the win lifts them out of the relegation zone to 10th place with 20 points from 21 games.
Barcelona must now regroup ahead of Sunday's high-profile Spanish Women's Cup semi-final showdown with last season finalist Atletico Madrid in edging closer to defend their diadem.