The top three seeds in the men's Sydney International draw were sent crashing on Wednesday, leaving Bernard Tomic and Juan Martin Del Potro on course for a rematch of last year's final.
Defending champion Del Potro, who was handed a wildcard after his ranking tumbled to 338th in the world following an 11-month injury lay-off, ousted top-seeded Italian Fabio Fognini 4-6 6-2 6-2 on Ken Rosewall Arena.
Second seed David Goffin lost 6-3 6-3 to Italian Simone Bolelli before Tomic accounted for German third seed Philipp Kohlschreiber 6-3 6-4 in the feature night match.
Del Potro brushed aside a code violation issued against him for taking too long between changeovers before marching into the quarter-finals.
The former US Open champion and world No.4 showed the benefit of concerted preparation by beating Fognini in an hour and 48 minutes.
Del Potro needed treatment from the courtside trainer during the first set but said there was no major discomfort from his left wrist.
He also said he had no issues with umpire Fergus Murphy, who took exception to his slow return to the court from a change of ends and issued the code violation early in the deciding set.
"It's my first warning on tour after my surgery," Del Potro said.
"He's a good umpire and it doesn't matter if he called warnings.
"This is my second match on tour after one year. I need to breathe more than the other players."
Fognini continually targeted Del Potro's backhand after the Argentine admitted earlier this week he was still managing the pain in his left wrist.
But he grew in confidence and precision as the match progressed, serving 11 aces and winning 80 per cent of points when his first serve was in play.
"My game is to serve strong and try and make winners with my forehand," he said.
"If my backhand is okay, I will be aggressive with it in the future.
"But now I think I just need to hit the ball as well as I can and don't try to make winners with my backhand.
"I just need to play a lot of backhands during the point, and if I do that I will get confidence very soon to play aggressive as well.
Poland's Jerzy Janowicz, who beat Nick Kyrgios in the first round, lost a three-set thriller against fifth-seeded Argentine Leonardo Mayer.
French fourth seed Julien Benneteau is the highest-ranked player left in the draw after beating Canada's Vasek Pospisil 7-6 (7-3) 6-3.
Tomic will play Gilles Muller for a place in the last four after the Luxembourg left-hander upset French seventh seed Jeremy Chardy 2-6 7-6 (7-1) 6-4.
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