Republic of Ireland remain unbeaten in 2018 World Cup qualifying after James McClean's second-half double secured a 3-1 win in Moldova.

Martin O'Neill's men had scraped past Georgia at home on Friday (AEDT), but appeared to be set for a comfortable victory when Shane Long netted inside two minutes.

However, with Ireland failing to turn their dominance into a second goal, Igor Bugaev struck an equaliser from Moldova's first chance just before the break.

The visitor's task was made somewhat harder as Long was withdrawn with an apparent hamstring injury, but it finally found its second goal through McClean, who had been crucial in setting up the opener.

McClean added another to seal the win, side-footing in from Seamus Coleman's centre.

Although Moldova - which has lost seven consecutive qualifying games - followed Georgia in giving O'Neill a scare, Ireland's return of seven points from three games has it handily placed in Group D.

Ireland broke the deadlock within two minutes as it immediately cut apart the home defence.

McClean leapt inside from the left and brought a long ball down into Wes Hoolahan's path, allowing him to slip through Long for a simple finish into the far corner.

Encouraged by the ease of the opener, the visitor came forward again, with McClean shooting straight at goalkeeper Nicolae Calancea and bundling another effort wide.

Glenn Whelan then lashed past the near post, but Ireland's momentum slowed as the game wore on and it was pegged back in first half stoppage-time.

Moldova captain Aleksandru Gatcan hopefully prodded forward, with Bugaev spinning onto the ball ahead of Shane Duffy and racing clear from the halfway line to tuck a shot low past Darren Randolph.

The home side quickly looked for a second after the restart, and Randolph did well to hold Alexandru Dedov's swirling strike from wide on the left.

Jon Walters then worked room to cross for McClean, but the winger's header was saved by Nicolae Calancea, and O'Neill dealt a further blow as Long hobbled off.

However, a second Irish goal finally arrived on 69 minutes.

James McCarthy thumped low into a crowded area, before Walters and McClean linked up again - the former controlling for the latter to sweep his finish into the net.

With Moldova now leaving gaps in search of another equaliser, a third goal followed with 14 minutes left on the clock.

Coleman made progress on the right to lift a delivery to the rampant McClean, who was unmarked at the back post and able to steer past Calancea to clinch the points.