Roger Federer saved seven match points to defeat Tennys Sandgren 6-3 2-6 2-6 7-6(8) 6-3 and reach the Australian Open semifinals for the 15th time.
Federer who had the upper hand in the first set trailed behind in the next two sets but astonishingly saved seven match points to take the game into the fifth set to seal a classic victory.
How it happened
The Swiss star got off to a bright start as he won the first set but world No 100 Sandgren rallied back to take the second.
Federer then suffered an injury in the third set after falling behind to an early break.The world No 3 let his frustration out at the umpire and called for a medical timeout.
It is unclear what the issue is but early suggestions are the 38-year-old was suffering with a lower-back problem.
And the injury clearly impacted Federer’s performance as his body language was subdued when he returned to Rod Laver Arena after a nine-minute break.
Sandgren only seemed to raise his game the more his opponent struggled and he won the third set with relative ease.
But Federer has proved over the years that he can never be ruled out and he saved three match points as they headed for a tiebreak.
Sandgren raced into a 6-3 lead but squandered a further four match points as Federer clung on to take the match to a decider.
And that is when the 20-time Grand Slam winner really clicked into gear as he ground out another impressive last-ditch win.
He remains unbeaten (15-0) in quarter-finals at this event and will next face second-seeded Serbian Novak Djokovic or No. 32 seed Milos Raonic of Canada.
Federer trails Djokovic 23-26 in their rivalry and has lost their past three matches in Melbourne, all of which took place in the semi-finals (2008, 2011, 2016). The Swiss leads Raonic 11-3 in their series and won their lone clash at this event in 2013.