The DR Congo international came to Rovers' rescue in the 93rd minute, turning to stab the ball home from six yards out after Andy Marshall failed to hold a shot from Keith Treacy.
That goal cruelly denied Coventry a famous giantkilling on this ground for the second time in as many years after they dumped Rovers out in the third round 12 months ago.
Coventry's hopes of pulling off a shock suffered an early blow when Rovers scored from their first attack in the second minute.
Paul Robinson launched a long free-kick into the visitors' penalty area and Samba nodded the ball down for Roque Santa Cruz, who promptly slammed an angled drive into the far corner from 12 yards out.
That goal visibly stunned the Sky Blues but they might have got back on level terms ten minutes later had Jordan Henderson showed slightly more composure when a chance fell to him inside the area.
However, as the half wore on it was Rovers who continued to pose the greater attacking threat.
Jason Roberts missed a golden opportunity to make it 2-0 when he volleyed wastefully wide after an incisive move involving Santa Cruz and Danny Simpson.
At the opposite end, Aron Gunnarsson was guilty of an even more glaring miss when he somehow headed wide from four yards out and with only Robinson to beat.
The Sky Blues emerged for the second half with renewed vigour and they got their just reward in the 61st minute as Gunnarsson atoned for his earlier miss in spectacular fashion.
Seizing on a headed clearance from Gael Givet, the Icelander controlled the ball on his chest 25 yards out before sending a scorching right-footed shot fizzing past Robinson.
Coventry's tails were up and Gunnarsson very nearly eclipsed that strike four minutes later after brilliantly skipping past three defenders before blasting wildly over.
However, the Sky Blues' noisy away following were soon celebrating again when Michael Doyle's speculative shot struck a defender and looped over a helpless Robinson in the 76th minute.
But the visitors were then crushed by Samba, who forced a replay with just seconds remaining.