An inspired Stefanos Tsitsipas roared back from a set down to end Roger Federer's reign as Australian Open champion and reach his first grand slam quarter-final.
Federer had not been beaten at Melbourne Park since losing to Novak Djokovic in the 2016 semi-finals, but Tsitsipas produced the biggest victory of his career to win 6-7 (11-13) 7-6 (7-3) 7-5 7-6 (7-5).
The 20-year-old Greek was given a time violation in the first game, yet was undeterred, saving all 12 break points he faced - including four set points in the second - to march into the last eight.
Federer beat Tsitsipas in their only previous meeting, at the Hopman Cup earlier this month, but the 14th seed was not broken in that contest and the rising star held his nerve on this occasion to break new ground.
The magnificent world number 15 hit 62 winners and made 36 unforced errors to the 20-time grand slam champion's 55 in an outstanding performance at a packed Rod Laver Arena on Sunday night.
Tsitsipas will now face Roberto Bautista Agut after ending Federer's quest to become the first man to win the tournament seven times and claim the 100th ATP tour title of his astonishing career.
Tsitsipas lost a serve after being given a second time violation in the first game, but showed great character to hold and settled quickly after a nervy start.
Federer complained to James Keothavong about a replayed point, suggesting the chair umpire felt bad about giving his opponent those early warnings, before the two let their tennis do the talking in a high-quality opening set.
The aggressive Tsitsipas took a 2-0 lead in the tie-break but Federer saved three set points, then won what was his fourth. However, a pulsating breaker ended on a slightly sour note as a spectator called 'out' during a point the defending champion won to take the set.
Both players continued to conjure up exquisite winners and the agile Tsitsipas dug in to hold in long back-to-back service games, the Swiss maestro failing to convert four break points.
Federer raced through his service games to keep the pressure on, but saw four set points come and go as the battling Tsitsipas dug deep yet again to hold at 5-5.
Tsitsipas made the 37-year-old pay for so many missed opportunities, continuing to come forward as he claimed the first two points of another breaker and won it with a searing forehand winner after being pegged back at 3-3 - Federer dropping a set for the first time in the tournament.
The bold Athens native frustrated Federer again by saving another two break points at 4-3 in the third set, slapping away a backhand winner to hold, and had his first two break points of the match in the next game but was unable to convert them.
Tsitsipas was not to be denied an elusive first break when Federer was serving to force another tie-break, though, the six-time champion netting a forehand to fall behind after arrowing a backhand wide.
Federer fans voiced their disapproval when Tsitsipas called for treatment on his cramping legs at 4-3 up in a tight fourth set, but the youngster continued to look sprightly and serve with conviction.
Tsitsipas made a blistering start to what seemed to be an inevitable third tie-break, Federer drilling a backhand long to trail 2-0 before rallying to level at 2-2 with an outrageous cross-court forehand winner.
Federer was unable to extend his 17-match winning run in the first major of the year, however, Tsitsipas dropping his racket in disbelief when an opponent 17 years his senior netted a backhand on the first match point.
Tsitsipas  bt Federer  6-7 [11-13] 7-6 [7-3] 7-5 7-6 [7-5]
Tsitsipas - 62/36
Federer - 61/55
Tsitsipas - 20/1
Federer - 12/0
BREAK POINTS WON
Tsitsipas - 1/3
Federer - 0/12
FIRST SERVE PERCENTAGE
Tsitsipas - 60
Federer - 67
PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Tsitsipas - 78/64
Federer - 79/61
Tsitsipas - 178
Federer - 166