Del Potro secures semi spot
Top seed Juan Martin del Potro edged Radek Stepanek 6-4 3-6 6-3 to progress to the semi-finals of the Sydney international.
The World No 5, playing in his first event of the year, sent down a total of 14 aces as he battled past the Czech veteran in two hours and eight minutes.
Del Potro fought back from a set down to beat Nicolas Mahut in the previous round and on Thursday was once again made to work hard for his win.
"I was positive for every moment of the match. Even when [Stepanek] improved his game during the second set, I was positive and waited for my chances," the Argentine told the ATP's official website.
Del Potro will face Dmitry Tursunov in the semi-finals, the fourth seed dominating behind a strong serve to take a 7-6 (7-5) 6-2 victory over Denis Istomin.
Tursunov said: "I had a pretty tight match against him in Cincinnati. I had multiple chances, but didn't capitalise on them, so hopefully I can use some of the information from that match to do a little bit better this time."
Defending champion and home favourite Bernard Tomic also progressed to the last four with a 6-4 6-3 victory over Alexandr Dolgopolov.
Tomic will next face Sergiy Stakhovsky, who defeated another Australian hope - Marinko Matosevic - 6-4 6-3.