Grégoire finished 12 points ahead of Dati in the first round of the election last Sunday, but the former culture minister made the race far more competitive by teaming up with center-right candidate Pierre‑Yves Bournazel, who finished a disappointing fourth.
The decision of far-right MEP Sarah Knafo to drop out of the race gave Dati another boost.
Grégoire chose not to team up with Chikirou on principle due to her party’s abrasive, confrontational approach to the local election. France Unbowed leader Jean-Luc Mélenchon has stoked controversy recently with his unapologetic response to the killing of a far-right activist, and later with comments that were condemned as antisemitic.
Jean-Cristophe Catalon contributed to this report.