Towering Argentine Juan Martin del Potro will play Russian Dmitry Tursunov in a semi-final of the Sydney International with the pair winning their quarter-finals on Thursday at the Olympic Park Tennis Centre.

Del Potro, the 2009 US Open champion who has worked his way back to world No.5 after an injury stretch in 2010, beat Czech Radek Stepanek 6-4 3-6 6-3.

With games on serve at 5-4, del Potro pounced in the first set, stealing a break to take it out.

But the wily Stepanek, who has featured in the top 100 for the past 12 years, kept del Potro on the hop in the second set with a break enough to even the ledger.

With his big serve and ripping crosscourt forehand, del Potro took charge in the decider though, again a single break of serve enough to secure the result.

The top seed has had thorough workouts in his two matches so far in Sydney, his first-up match against Nicolas Mahut also going three sets.

Tursunov enjoyed a 7-6 (7-5) 6-2 win over Uzbek Denis Istomin.

Bernard Tomic and Marinko Matosevic could set up a dream all-Australian semi-final if the pair win their quarter-final fixtures on Thursday night.

Defending champion Tomic takes on Ukrainian Alexandr Dolgopolov while wildcard Matosevic plays qualifier Sergiy Stakhovsky.