But any off-court distractions he managed to put to one side in a relatively low-volume display sprinkled occasionally with the instinctive shot-making that makes him such a draw.
As in his five-set win over American Brandon Nakashima in the previous round, Kyrgios kept his volatile temperament under wraps, although he regularly lambasted his sizeable entourage as the match dragged on, calling for more support.
Once again his serve underpinned his game, digging him out of trouble whenever Garin threatened to drag himself back into a contest that drifted away from him after his fast start.
Kyrgios saved eight of the nine break points he faced, including two at 4-4 in the first set.
Garin, who beat Kyrgios's compatriot Alex De Minaur from two sets down in the previous round, battled hard to extend the third set to a tiebreaker and led 5-3 in it before Kyrgios hit back to win the last four points.
One of tennis's great enigmas will now face Nadal in the semi-finals, a clash he predicted would be "probably the most-watched match of all time."
World number 40 Kyrgios, the lowest-ranked semi-finalist at Wimbledon since Marat Safin (75) and Rainer Schuettler (94) in 2008, will start as underdog, but will relish the occasion.
"I never thought I'd be in the semi-final of a Grand Slam. I thought that ship had sailed -- that I may have wasted that window in my career," he said.
"I had lost the love, lost the fire, lost the spark. Then some things just changed in my life. I kind of just rediscovered that I've got a lot of people that want me to play, that I play for. I've got a lot left in the tank."
Kyrgios has been almost meek and mild since his explosive third-round clash with fourth seed Stefanos Tsitsipas, after which his opponent called him a bully with an evil side.
He has let his tennis talk and, more importantly, shown a focus many thought was beyond him.
Even after a slow start on Wednesday there was no negativity and he broke back to level at 3-3. Garin got lucky with a net cord to get two break points at 4-4 but the Australian slammed the door shut and then broke to love as Garrin cracked.
Kyrgios broke early in the second set and saved break points at 3-1 and 4-2 before sealing the set with an ace -- one of 17 he fired past the south American.
The third set was tight but Kyrgios always had another gear.
Garin believes Kyrgios could go all the way.
"I played all of the great serves on the Tour -- and for me he's the best server," the 26-year-old said.
"He has great chances to win the tournament."