Martin O'Neill's side started brightly, enjoying plenty of possession and almost taking the lead when Robbie Brady's free kick was headed onto the bar by Ciaran Clark.

Robbie Keane of Republic of Ireland celebrates after scoring Ireland's 3rd goal during the UEFA EURO 2016 Qualifier between Gibraltar and Republic of Ireland at Estadio Algarve on September 4, 2015 in Faro, Portugal. © Getty Images

Robbie Keane also went close in the opening stages as Brady's pass found the Irish forward, but he failed to direct his shot the right side of the post.

However, the Boys in Green did take the lead on 26 minutes when Cyrus Christie was allowed to cut inside from the right flank, and his toe-poke at goal looked to have deceived Jordan Perez as the Gibraltar keeper could only watch the ball roll into the net.

Jonathan Walters nearly added a second soon after as the Stoke City forward unleashed a dipping 30-yard shot, which Perez managed to turn over his own crossbar.

Cyrus Christie of Republic of Ireland celebrates with teammates after scoring Ireland's 1st goal during the UEFA EURO 2016 Qualifier between Gibraltar and Republic of Ireland at Estadio Algarve on September 4, 2015 in Faro, Portugal. © Getty Images

Gibraltar's best period came towards the end of the first half when Shay Given needed to stop two efforts from Liam Walker in quick succession.

The minnows fell further behind soon after the restart when Erin Barnett's attempts to block a cross saw him divert the ball onto the left post and, with Perez beaten, Keane was on hand to tap home from no more than a yard out.

Within two minutes, Ireland were awarded a penalty after Walker managed to bring down Wes Hoolahan in the area.

Ireland's forward Robbie Keane (R) vies with Gibraltar's defender Joseph Chipolina during the Euro 2016 qualifying football match Gibraltar vs Republic of Ireland at the Algarve stadium in Faro on September 4, 2015. © Getty Images

Keane duly stepped up and slotted the ball into the corner as the visitors wrapped up victory.

They added a fourth on 79 minutes when Shane Long headed Jeff Hendrick's cross into the top corner as Ireland leapfrogged Scotland in the Group D standings.