Midfielder Joe Allen’s second in as many matches had set the Reds on their way to a home meeting with West Ham a week on Saturday but it was members of Jurgen Klopp’s reserves who finished the job.
The way in which teenage substitute Ojo, recalled early from a loan spell with Wolves, curled a brilliant effort past Bobby Olejnik provided a lesson in finishing for an out-of-sorts Christian Benteke who looked anything but a £32million Belgium international against a League Two defence.
Klopp made three changes from the scratch side he fielded in the previous tie, bringing in some experience in goalkeeper Simon Mignolet, Allen and Jordon Ibe while handing Tiago Ilori, Brad Smith and Kevin Stewart their senior Anfield debuts.
Confidence shown by the likes of youngsters Joao Carlos Teixeira, whose sublime cross with the outside of his right foot was among his many contributions, Cameron Brannagan and Brad Smith was not so evident in Benteke.
He was hailed pre-match by Klopp as “a complete striker” as the German offered a defence for the summer signing’s troubles but he looked far from it.
His one telling contribution of the first-half was to exchange passes with Smith to allow the Australian to cross for Allen’s goal in a well-worked move and he also had a hand in Teixeira’s goal late on.
There were far more entries in his debit column, however, as he failed to impose himself on a League Two defence and failing to hit the target with his close-range header from an inviting Teixeira cross - a chance he used to put away with his eyes closed for Aston Villa - highlighted his troubles.
There were other examples though: a mis-hit shot from the edge of the penalty area, a free header into the side-netting, a mis-control knocking the ball out for a goal-kick prompting ‘What a waste of money’ chants from visiting fans in the Anfield Road end and - with the last chance of the game - fluffing his lines after rounding Olejnik on the counter-attack.
For a man of such physical size Benteke was also out-muscled too easily, with Troy Brown easing him off the ball as he charged through on goal in the second-half.
Around him others continued to flourish with Allen scoring in back-to-back games for the first time since October 2011 for Swansea when he converted Smith’s cut-back, having snatched a last-minute equaliser against Arsenal a week ago.
Either side of half-time Ibe fizzed one shot just over and had another clawed back from almost behind the line by Bobby Olejnik.
But the goalkeeper could do nothing about Ojo’s superb individual 75th minute strike as he shifted the ball onto his left foot and curled a shot into the far top corner.
With Exeter, who managed just one shot on target and barely threatened, tiring fast, fellow substitute Teixeira benefited from some nifty footwork from Benteke to cap a memorable night for Klopp’s youngsters.
The other positive of the night was the return of Jon Flanagan as a second-half substitute 619 days after his last appearance after recovering from two knee operations.
Mignolet, Randall (Flanagan 51), Tiago Ilori, Jose Enrique, Smith ,Brannagan, Stewart, Allen (Ojo 65), Ibe (Chirivella 79), Benteke, Teixeira.
Olejnik, Ribeiro, Brown, Moore- Taylor, Woodman, Butterfield (Hoskins 46), Nicholls, Oakley (Wheeler 64), Davies, Holmes, Morrison (Nichols 46).