The Grecians were the better side for the majority of the match, but couldn't find a way past Forest Green goalkeeper Luke McGee.
Rovers extend their lead at the top of the EFL League Two table to eight points by keeping their tenth clean sheet of the season.
Story of the game
Exeter came out on the front foot, Jevani Brown narrowly curling over the bar, but they should have been in front on nine minutes.
Brown flicked the ball into the path of the onrushing Matt Jay, who played it to Josh Key, his shot from a narrow angle going just wide from six yards out.
At the other end, Forest Green created one of their very few chances, a teasing cross by Nicky Cadden set to find Jamile Matt only to see Chieck Diabate get an outstretched leg to it.
Chances continued to come for the visitors, Padraig Amond coming close to nabbing the opener, but he couldn't power his header home from a Jake Caprice while Key curled inches wide moments later in stoppage time.
The second half saw more opportunities, Cadden seeing his free-kick whistle just past the post while McGee stopped Collins' shot from the edge of the box.
Just before the hour mark, a well-worked corner by the Grecians from Collins found Dieng, but the Frenchman headed over from six yards out.
McGee made a double save in the final 20 minutes, stopping Jay's long-range shot and holding on to a deflected effort by Dieng from distance.
The Forest Green ‘keeper then denied Dieng once more with his knee after the had sent a downward header on goal.
The hosts had their best chance in the closing stages of the game, Mathew Stevens heading over from a corner.
Man of the match: Luke McGee
The Forest Green goalkeeper was superb, making several important saves in a match where the defence in front of him often let him down.