Canada needs just one victory in the two Sunday singles matches at the University of British Columbia to advance to the world quarter-finals for the second time. Milos Raonic, ranked sixth in the world, will play No. 4 Kei Nishikori in Sunday's first match. Pospisil is scheduled to play Tatsuma Ito.
"You are playing Davis Cup and you have to expect they are going to play their best," said the Toronto native, who is ranked No. 5 in doubles.
"Sometimes I get a little frustrated because you want to go more straight forward. There is a reason you are ranked higher and you want them to fold. That doesn't happen."
The doubles match was a back-and-forth affair with Canada winning the first set and then each side alternating victories into the fifth set. It was tied at 3-3 midway through the deciding set before the 42-year-old Nestor served for the lead and Japan double-faulted in the eighth game to put Canada up a break.
The 24-year-old Pospisil, from Vernon, B.C., closed out the match with four straight points much to the delight of a partisan crowd at the Doug Mitchell Thunderbird Sports Centre.
Canadian coach Martin Laurendeau said his team is where it wanted to be.
"You have one more match to win but it's often the toughest one," said Laurendeau. "Everyone would rather be up 2-1 than down 2-1.
"Hopefully it allows Milos to breathe a little easier and lets him begin the match a little more relaxed so he can be loose and play the game a little bit more comfortably."
Laurendeau wasn't surprised by the fight shown by Soeda and Uchiyama.
"It's Davis Cup, guys come out swimming," he said. "When you are the underdogs, one of the ways to approach the match is go for the win. You have everything to gain."