Owusu, who made his debut for the first team on Saturday as a reward for eight goals in three reserve games, was given an extended spell as sub at the Crabble when he replaced Mark West in the 67th minute.
His golden moment seemed to have come with seven minutes left when he put the faintest of touches on Danny Bolt's comer to help it into the net, but while his teammates rushed to congratulate Owusu in the back of the net, the referee ruled out the goal for handball and the match went on to finish all square.
But it could have been a different story altogether had Dover's ace marksman David Leworthy not fluffed a penalty in the 24th minute. Leworthy's strike partner Ricky Reins, who this time last year was tormenting Windsor in the FA Vase for Folkestone Invicta, created havoc in the Slough box, and when the ball rolled out to Gerry Dobbs at the edge of the box, Byron Walton caught his feet and Mr Pettitt pointed to the spot.
But Leworthy appeared to rush the kick, and the resulting shot clipped the top of the bar and flew over the stand and quietly into the night. The woodwork had barely time to recover though, as lain O'Connell's effort from a deep cross hit the post three minutes later, and suddenly the Rebels, who had faded after a bright opening, were spurred into action.
West could have put the Rebels ahead in the 33rd and 37th minutes with headers, but on each occasion Brian Horne was up to the challenge and saved well. Dover made the brighter start to the second-half, with Stuart Munday's 48th minute cross hitting the base of the far post, and a second, drilled centre from the same man forcing Ben Miles to desperately scoop the ball away.
The game finished in lively fashion, with Miles making a fantastic reflex save to claw away Munday's close range blast and preserve his third clean sheet in four games.
But the Rebels finished the stronger, Bolt's 25-yard freekick whizzing past the post in injury time before Byron Walton blasted over from the edge of the box with the last kick of the game.
Walton, preferred to Bolt and Mark Fiore after some eye-catching substitute appearances, was also one of three Rebels booked on the night as a harder edge to Slough's play became apparent. Having become Conference top dogs, they will need those battling qualities if they want to stay, there.
Dover Athletic Lineup
Home, Munday, Barber, Thoodosiou, Daniels, O'Connell, Stebbing, Dobbs, Reina, Leworthy, Strouts. SUBS: Budden, Lindsay (for Reina, 67), Pilkington