Two aces and a victor gave Kyrgios, Australia's No. 1 player, the win over Struff in 1 hour, 37 minutes.
Trailing 2-1 in the Cup tie against Germany at Brisbane's Pat Rafter Arena, Kyrgios carried Australian hopes as he took the court against long-time junior rival and world No 5 Alex Zverev.
"They are the things Nick does which the public doesn't see".
OVERSEAS tournament directors will likely offer Alex de Minaur ATP wildcard opportunities this year after his high-profile summer, Australian men's tennis performance director Wally Masur says.
Zverev had other ideas.
World number 22 Fognini edged past Sugita 3-6 6-1 3-6 7-6 7-5 in a marathon match lasting four hours and eight minutes to take Italy into the quarter-finals for the fifth time in six years.
Hewitt claimed Kyrgios remained a future doubles option for Australia - but admitted it was easier said than done. A frustrated Kyrgios was given a point penalty in the tie-break for smashing his racquet and was unable to pressure the World No. 5 in the third set.
Australian captain Lleyton Hewitt hinted he might have played in Saturday's doubles but resisted the temptation, pairing Ebden with world No.4 doubles specialist Peers.
The mercurial Kyrgios, who has responded well to the Davis Cup captaincy of Lleyton Hewitt, was in sublime touch against Struff. "We showed that we are able to go further than this".
"It's an incredible feeling, hopefully this is just the beginning for us", the fifth-ranked said.
"They didn't play the best match they could have played but they still fought, but came up short - I wasn't thinking about that at all".
The visitors sprang a late change, replacing Peter Gojowczyk with Jan-Lennard Struff.
"I felt it the day after I played my first match. They know they can't win without me and I know they can't win without me", the three-time ATP victor said.
But Taro Daniel, ranked a lowly 100 in the world in singles, put up a fearless fight against the much higher ranked Fabio Fognini in a marathon first match in the compact Morioka Takaya Arena.
"It obviously affected me a lot", Kyrgios said.
"My serve is my biggest strength".
Tomic, who had represented himself as the youngest ever player for Australia in Davis Cup in 2010, hasn't had the greatest of forms recently.