On paper, Japan always looked likely to struggle without talisman Kei Nishikori, who is just returning from a wrist injury that had sidelined him for five months.
But Taro Daniel, ranked a lowly 100 in the world in singles, put up a brave fight against the much higher ranked Fabio Fognini in a marathon first match in the compact Morioka Takaya Arena.
The Italian, now ranked 22 in the world, went two sets to one down after a remarkable comeback from Daniel in the third set from 4-2 down.
But the 30-year-old, who has five ATP titles under his belt, showed his experience to clinch the last two sets for a 6-4, 3-6, 4-6, 6-3, 6-2 win to get former Davis Cup champions Italy off to a flying start after a gruelling four hours.
The second match pitted world number 41 Yuichi Sugita against veteran Andreas Seppi, now ranked 78, in what turned out to be a thrilling rollercoaster of a match.
Sugita looked to have the match sewn up at 4-2 up in the deciding fifth set and had break points to take a 5-2 lead with his serve to come.
But the 33-year-old Seppi, once a top-20 player, clung on to held his serve and then secured a break of his own, taking the match to a nailbiting climax.
Seppi had a match point on the Sugita serve at 6-5 but the Japanese player saved it and took the match into a tie-break.
Sugita raced into a 3-0 lead in the tie-break and despite brilliant retrieving from Seppi, closed out the match to rapturous applause from the home fans 4-6, 6-2, 6-4, 4-6, 7-6 (7-1) after three and a half hours.
Saturday's doubles sees Yasutaka Uchiyama and New Zealand-born Ben Mclachlan take on Simone Bolelli and Paolo Lorenzi, as both teams try to grasp the initiative in the tie.
Japan are looking to reach the quarter-finals of the Davis Cup for only the second time after Nishikori helped them reach the last eight in 2014.
Italy were champions back in 1976 and have finished runners-up on six occasions.