Striker Leigh Griffiths led the line for Neil Lennon's side after making a playing return during the Hoops' pre-season trip to Austria, and the Scotland striker was a thorn in the French team's side in the opening exchanges as he hassled and harried the Rennes rearguard.
Lewis Morgan was also handed a starting berth as a number of fringe players featured from the start, and the former St Mirren winger impressed on the right flank.
Ewan Henderson created the first real chance of the game, taking the ball from Scott Sinclair on the left before jinking inside and hitting a curling effort which Rennes 'keeper Tomas Koubek was equal to.
The visitors launched a counter-attack of their own almost immediately but Anthony Ralston did well to track Clement Grenier and block the former Lyon man's effort.
Rennes continued to probe but found first-time central defensive pair Jullien and Nir Bitton in impervious form.
Henderson conjured up another chance for Celtic just after the half-hour mark, winning a corner that was cleared by the Ligue 1 side before exchanging passes with Sinclair and firing in a decent effort that required a smart save from Koubek.
Lennon made just two changes at the interval, introducing Stephen Welsh for Bitton and replacing Brown with Callum McGregor, who assumed the captaincy.
Rennes fielded an entirely different team for the second period and the French side pressed hard for an opener in the early stages of the half.
Craig Gordon had to be alert to foil Diafra Sakho from point-blank range after the former West Ham striker sprang the offside trap around ten minutes after the break.
Lennon introduced Kristoffer Ajer for Jullien, Connor Hazard for Gordon and Ryan Christie for Connell just before the hour mark and the latter went close from Jonny Hayes cross as the home side continued to ask questions of the Rennes defence.
Henderson continued to impress and his cut-back for Sinclair forced Jeremy Gelin into a fine block to keep the scoreline goalless.
Henderson lobbed the loose ball back into the box but his cross was just too high for Sinclair at the back post, who just failed to connect with the ball.
At the other end, Hazard's first real taste of action was a straightforward save from Lucas Da Cunha's effort from distance.
James Forrest was given the last 20 minutes, replacing the impressive Morgan before Lennon, perhaps with one eye on next week's Champions League qualifying second leg against FK Sarajevo, introduced Karamoko Dembele, Odsonne Edouard, Calvin Miller, Scott Robertson and Grant Savoury for Sinclair, Griffiths, Hayes, Henderson and Ralston.
The catalogue of changes interrupted Celtic's flow and Rennes twice went close in the final ten minutes.
Ajer threw himself in front of Adrien Hunou's effort with five minutes remaining while Da Cunha threatened again with a vicious shot in the 88th minute which whistled just past Hazard's post.
Edouard had a glorious chance to snatch an injury-time winner for Celtic after being played in by Christie, but the former Paris Saint-Germain forward's chipped effort was cleared off the line.
Celtic: Gordon (Hazard 57); Ralston (Savoury 86), Bitton (Welsh 46), Jullien (Ajer 57), Hayes (Miller 86); Brown (McGregor 46), Connell (Christie 57), Morgan (Forrest 70), Henderson (Robertson 77), Sinclair (Dembele 77); Griffiths (Edouard 77).
Rennes (first half): Koubek, Boey, Da Silva, Johansson, Grenier, Siebatcheu, Lea Siliki, Maouassa, Lauriente, Tait, Poha.
(second half): Salin, Nyamsi, Diallo (Gboho 77), Da Cunha, Bourigeaud, Rutter, Camavinga, Soppy, Hunou, Gelin, Trouillet, Sakho.