However, Shane Long headed home a fourth in the final quarter to put gloss on the win and reinvigorate their qualification bid.
Here, Sports Mole reviews how the game was won.
© Getty Images
On target: 4
REPUBLIC OF IRELAND
On target: 14
Was the result fair?
Undoubtedly. The only question lingering over this affair was how many the Irish would win by. It was four in the end, but on another night it might have been double that. As expected, the Boys in Green were utterly dominant and the result is not up for debate.
Pre match, Martin O'Neill was unequivocal in his assertion that Gibraltar had improved since their 7-0 demolition in Dublin 11 months ago. On this evidence, the Ireland boss has a point. Through a combination of decent defending and riding their luck, the hosts only managed to concede once in the first half, with goalkeeper Jordan Perez also pulling off a number of smart stops to atone for his howler in the reverse fixture.
At the other end, Liam Walker - one of three professionals in the squad - managed to sting the gloves of Shay Given with two first-half efforts that had Irish hearts in mouths momentarily - something they failed to do in Dublin.
However, Perez's good work was undone after the break when his error allowed Keane to double the advantage after failing to deal with Jon Walters's harmless cross. Minutes later, Walker then fouled Wes Hoolahan to concede a penalty as Ireland led 3-0 by 51 minutes.
Gibraltar had one or two promising attacks after that, and might have even scored if not for Robbie Brady's superb last-ditch tackle to stop John Sergeant in his tracks. In the end, they lost by four, but they certainly look like a nation on the up - even if the ascension is more baby steps than leaps and bounds.
Republic of Ireland's performance
The cricket score envisioned for the Republic of Ireland looked a little optimistic by half time following a first 45 minutes in which the visitors only scored once. It was right-back Christie who showed tidy fleet of foot to evade a few challenges, before poking an outside-of-the-boot effort past Perez from an acute angle - an excellent goal even if it was 'only' Gibraltar.
Brady's wand of a left foot created a number of chances before and after the goal, with the Norwich City man arguably the best player on the pitch in the first half. First, Brady's excellent free kick was headed against the crossbar by Ciaran Clark, before another fine ball found Keane, whose first-time volley rippled the side-netting.
The emphatic victory envisioned for O'Neill's side began to take shape after the break. Keane tapped home on the line for perhaps the easiest of his 66 goals in a green shirt, following a dreadful error by Perez, before the Irish talisman added a third minutes later from the penalty spot.
From there, Ireland - who scored all seven of their goals before the hour mark in the reverse fixture - took their foot off the gas, with O'Neill's three substitutions affecting the fluency to a degree. However, Long managed to add a fourth in the final quarter by heading home Jeff Hendrick's excellent ball to cap a fine win.
The margin of victory was not as handsome as some predicted, but it was more than enough to take them third in Group D, following Scotland's setback in Tbilisi, and O'Neill will care about little else.
Sports Mole's man of the match
Robbie Brady: The ex-Hull City man was far and away the game's best player on a night where none of his teammates really stood out, with the left-back producing fine contributions at both ends and in both halves. Whether Ireland needed the silk of his left-footed deliveries, or the steel of his last-ditch challenges, Brady was the man for both.
It has to be goalkeeper Perez, who allowed Walters's harmless cross squirm beneath him before Keane tapped home the second from close range. Perez - a full-time fireman - had plenty of good moments, but that error is what his performance will be remembered for.
Marijo Strahonja did not have an overly difficult game to officiate tonight. He only had three players to book - Kyle Casciaro, Walters and Erin Barnett - and all looked the correct decision. With no moments of controversy or contentious decisions, the Croat can be pleased with his performance.
Gibraltar: The minnows face Poland away on Monday.
Republic of Ireland: The Irish now turn their attention toward another must-win clash with Georgia in Dublin on the same day.