Seven days on from his side's impressive thrashing of South Africa, Ireland coach Joe Schmidt made 13 alterations to his starting XV but initially watched on with comfort as tries from Darren Sweetnam, Dave Kearney and Jack Conan put the hosts in command.
Fiji refused to give in, however, and pulled level when Henry Seniloli's eye-catching score was followed by Timoci Nagusa intercepting a Kearney pass to go over in the 45th minute.
There were no further tries, but Ireland sneaked home courtesy of a second penalty from replacement fly-half Ian Keatley, whose first three-pointer had been cancelled out almost immediately by Ben Volavola.
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Joey Carbery, the man Keatley came on for with 16 minutes remaining, shone in the first period for Ireland and laid on the first try for Sweetnam after breaking the Fiji line with a delightful step inside.
Although Volavola kicked a penalty in response, Ireland looked capable of recording a handsome win when Kearney went over on the left and Conan broke clear from halfway to touch down following one of Fiji's many handling errors.
However, the visitors' enterprise was rewarded when a thrilling counter-attack saw Nemani Nadolo collect his own kick and cut inside to put Seniloli over for a try Volavola converted with the last action of the half.
Nagusa then telegraphed an ill-advised pass from Kearney and Volavola again added the extras to level the scores.
It was therefore left to Keatley to seal victory for Ireland, his second successful kick coming after Kini Murimurivalu had been penalised for a lifting tackle on Cian Healy.
Photo Getty Images. Caption: Ireland number eight Jack Conan