Croatian Marin Cilic has produced one of the upsets of the tournament to dump US Open champion Juan Martin del Potro from the Australian Open in a five-set marathon.
The two youngest remaining players in the draw slugged it out for more than four-and-a-half hours before the 14th seed prevailed 5-7 6-4 7-5 5-7 6-3 to advance to his first quarter-final at Melbourne Park.
Little separates the pair on paper- they are both 21, born just five days apart, and stand 198cm tall - and it was the same on Hisense Arena in an epic struggle on Sunday night.
After splitting the first four sets, Del Potro was clearly feeling the pinch from his second five-setter of the week, having beaten American James Blake 10-8 in the decider in the second round.
The Argentine world No.4 beat Cilic on his way to the title at Flushing Meadows last year and also won their quarter-final clash at Melbourne Park.
Del Potro came into this tournament hampered by a wrist injury that forced him to withdraw from the AAMI Classic at Kooyong in the week leading into the year's first Grand Slam.
Cilic, who beat Australian Bernard Tomic in a second-round match that did not finish until after 2am, successfully defended his title in Chennai to start 2010 with his win over del Potro stretching his unbeaten run this year to nine.
Cilic will meet either American seventh seed Andy Roddick or 2007 finalist Fernando Gonzalez in the last eight on Tuesday.