Beaten Kyrgios may have played his last Australian Open singles
The combustible home hero was grimacing from an abdominal injury and fired expletives at his coaching box as he was bundled out by Britain's Jacob Fearnley 7-6 (7/3), 6-3, 7-6 (7/2) on his favourite John Cain Arena.
"Realistically I can't really see myself probably playing singles again here," a crestfallen Kyrgios, 29, told reporters.
"I didn't want to just throw in the towel and walk off or retire.
"I was hurting physically. I respect my opponent. The fans waited hours to come see me play."
Fearnley managed to subdue Melbourne's notoriously noisy night crowd with a controlled victory over the 2022 Wimbledon finalist.
"I'm sorry for Nick," said Fearnley. "I could tell he was dealing with some stuff."
The Australian only made his comeback after 18 months out in Brisbane earlier this month following knee surgery and wrist reconstruction.
Kyrgios withdrew from an exhibition match against Novak Djokovic four days ago with an abdominal strain, raising fresh concerns about his fitness.
The worries were confirmed when, in his first Australian Open match since 2022, Kyrgios spoke to physios multiple times in the second set after wincing in pain while serving.
"With my physical state going into the match, I knew that I was going to be really hindered with my serve," said Kyrgios.
"But just seeing the fans line up for four, five hours, just the amount of people that were there supporting me, it was hard to kind of throw the towel in.
"Would have been really easy to kind of just roll over.
"It's obviously heartbreaking because I feel like my level's there," added Kyrgios, who confirmed that he would still play doubles with fellow Australian Thanasi Kokkinakis.
"We've won this event before. We owe it to each other I think to go out there in front of the crowd and have a bit of fun."
Tirade
In the first set opportunities to break were scant as big serving dominated, until world number 92 Fearnley won the tiebreak to quell the rowdy crowd.
"I knew I wasn't going to be able to get you guys on my side," Fearnley told the fans.
"So I was just trying to focus on myself. I think all things considered, it's probably the best match I've ever played."
Kyrgios exploded into a verbal tirade in his team's direction but Fearnley, in only his second Grand Slam appearance, refused to be intimidated and broke early in the second set.
Kyrgios had one final flourish for his fans at the end of the third set.
Clearly in pain, he fashioned a set point as Fearnley served at 4-5 but could not convert.
Fearnley, who clinched the match on another tiebreak to progress in 2hr 19min, will now face Arthur Cazaux of France.
It sealed only the third ATP main Tour match win for Fearnley, who lifted four Challenger-level titles last year.