Coventry's last game at their own stadium was a 1-0 defeat against Leyton Orient on April 20, 2013, with a dispute between the club and stadium owners Ricoh – an electronics company – creating intense friction.
During their exile, Coventry played their home matches at Northampton Town's Sixfields, some 28 miles away from their own city.
However, they were back on true home soil on Friday and they gave the 27,306 supporters in attendance a return to remember with a battling win courtesy of Frank Nouble's early goal.
Steven Pressley's men got off to an excellent start as they were urged on by their noisy and expectant home crowd.
O'Brien went close in the fifth minute as he sent an overhead-kick just wide, and Coventry did not have to wait long to break the deadlock.
After a clever team move, debutant Nouble, on loan from Ipswich Town, produced a fine left-footed finish to send the home fans into delirium after just 10 minutes.
Nouble was involved again in the 22nd minute, but on this occasion Conor Thomas was unable to beat Stephen Bywater in the Gillingham goal after latching on to the former Chelsea man's clever back-heel.
The visitors struggled to craft chances and Coventry almost doubled their lead with 25 minutes to go, but John Fleck's long-range half-volley from out wide was clawed away by Bywater.
Gillingham piled on the pressure in the closing stages, ensuring a nervous final 10 minutes for the Coventry supporters.
However, Pressley's charges battled to hold on and they clinched their second win of the season to celebrate a landmark occasion in style.
