The scrum-half then sniped over from a five-metre scrum to score the first try of the match and although he missed the conversion a second penalty gave the fired-up visitors an 11-3 lead after 11 minutes.
Sexton slotted over his third conversion and made it four out of four after Kearney slid under the tackles of two Fijian players to score Ireland's fourth try with four minutes of normal time remaining.