Romain Hamouma looked to have earned Les Verts a point when he equalised four minutes into the second half, cancelling out Belgian midfielder Yannick Ferreira Carrasco's 15th-minute opener at the Stade Louis II.
But Ocampos, on as an 84th-minute replacement for Ferreira Carrasco, had other ideas and wasted no time in turning the game in the hosts' favour.
The win moved Claudio Ranieri's side three points clear of champions Paris Saint-Germain and four ahead of third-placed Marseille ahead of the two sides' blockbuster clash at the Stade Velodrome on Sunday night.
Lille moved up to fourth in Ligue 1 as they dismantled Ajaccio.
Pape Souare's header was all the hosts had to show for a first half of utter dominance and the one-way traffic continued after the break, yielding two more goals.
Salomon Kalou created the first for Idrissa Gueye and then netted the third himself to complete at 3-0 success which moved Lille level on points with Marseille.
Filip Djordjevic scored a first-half double to set up a comfortable 3-0 home win for Nantes over Evian.
Djordjevic found the net in the second and 34th minutes as Nantes took a two-goal lead into the break before defender Papy Djilobodji sealed the win shortly after the hour mark.
The result sees Nantes move up into fifth while Evian slip to 15th.
Valenciennes were spared an eighth defeat in nine Ligue 1 matches as Eloge Enza Yamissi's stoppage-time strike pegged back Reims at Stade du Hainaut.
The league's bottom side were on course to draw yet another blank when Prince Oniangue fired the visitors in front after half an hour, but Enza Yamissi's last-gasp leveller earned them a deserved share of the spoils in a 1-1 draw after seeing Reims goalkeeper Kossi Agassa put on an inspired display.
Valenciennes began the season with a 3-0 defeat of Toulouse, but a run of seven straight defeats left confidence at a low ebb and coach Daniel Sanchez will be a relieved man to finally stop the rot.
Second-half goals from Jeremy Sorbon and Mustapha Yatabare helped Guingamp to their second win in three Ligue 1 games as they edged to a 2-0 victory over 10-man Rennes.
Sorbon opened the scoring three minutes after the interval, while their cause was helped greatly by Portugal international Nelson Oliveira's dismissal just after the hour mark.
Yatabare ensured there was no way back for Rennes as Guingamp made their one-man advantage pay and bounced back from last week's defeat at Nice in style.
Toulouse beat Nice 1-0 in the day's other match, Wissam Ben Yedder with the only goal after 34 minutes.