Junior Dale opened the scoring for Nancy, but Mickael Le Bihan turned swiftly after Younes Belhanda had played him through and side-footed a low effort beyond Cameroonian shot-stopper Guy N'Dy Assembe to open the scoring after only 36 minutes.
With Mario Balotelli suspended and Alassane Plea out with injury for the remainder of the season, the inclusion of Le Bihan proved to be paying dividends for Lucien Favre as the forward netted his third goal of the season.
Early in the second half, Nice deservedly doubled after Issiar Dia clumsily fouled Dalbert inside the box to concede a penalty which Seri stepped up and converted for his first of the night.
The Ivory Coast international then raced from midfield and latched onto Valentin Eysseric's pass before firing past N'Dy Assembe in the 84th minute to earn Favre's men a UEFA Champions League spot whilst they are also four points off top spot.
The strikes were Seri’s fifth and sixth of the season in 29earances.
Nice remain unbeaten at home this season and this was their 13th win in their 17th league match at the Allianz Riviera.