The two remain separated by just a point after scoring a goal apiece in the space of six second-half minutes, leaving Monaco third and their visitors one spot below them.
Following a goalless first half, Leonardo Jardim's side conceded their first Ligue 1 goal at the Stade Louis II since November's 2-2 draw with Caen.
Mevlut Erdinc angled a header from Franck Tabanou's cross that left Danijel Subasic with no chance two minutes after the hour.
However, Martial had the final say when he crashed home a volley to ensure a draw.
Layvin Kurzawa crossed from the left and Martial stole in unmarked to hammer an effort past Stephane Ruffier, registering his fifth goal in as many games in the process.
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