Del Potro battles past Mahut
Top seed Juan Martin del Potro fought back from a set down to take a 1-6 6-3 6-4 victory over Nicolas Mahut in the second round of the Sydney International.
The Argentine was playing his first match of the year and made a sluggish start before turning things around to win after 1 hour 51 minutes of action.
Del Potro broke in the seventh game of the deciding set and finally made it over the line after saving two break point chances in the following game.
"For my first match in two months it was okay. The court and the balls are really fast and it's tough to play long rallies," del Potro said.
"Mahut serves really well and he played a lot of slices and volleys, so it was tough to feel the ball on the baseline.
"In the end I broke his serve in the third set, only once, and that was enough to close the match."
The world No 5 will face Radek Stepanek in the quarter-finals after the Czech player was a 6-2 7-6 winner over lucky loser Albert Ramos.
Del Potro added: "They (the Czech Republic) won the Davis Cup, so he must feel confident playing on this surface. He has experience. We play many times. Every match was close.
"I need to improve my game a little bit from the start of the match and then see what happens."
Elsewhere in round two, second seed Jerzy Janowicz was dumped out after Alexandr Dolgopolov defeated him 6-2 6-2 in under an hour.
Third seed Andreas Seppi also bowed out on Wednesday, home wildcard Marinko Matosevic recording a 6-3 6-4 victory over the Italian.
Another Australian hope, defending champion Bernard Tomic, battled past Blaz Kavcic 6-3 4-6 6-4 to set up a last-eight clash with Dolgopolov.
There were also wins for Denis Istomin and Sergiy Stakhovsky, who defeated seventh seed Marin Cilic and No 6 seed Julien Benneteau respectively.