Argentine top seed Juan Martin del Potro has joined Australian No.3 Marinko Matosevic in the quarter-finals of the Sydney International.

Australian Open smokey Juan Martin del Potro has an equipment crisis, revealing he’s down to just two racquets five days out from the season-opening grand slam in Melbourne.

Del Potro overcame a sluggish start to his season to progress to the quarter-finals of the Sydney International with a 1-6 6-3 6-4 win over Nicolas Mahut in his opening match of the year.

The former US Open champion next faces Radek Stepanek on Thursday for a spot in Friday’s semi-finals after the Czech Davis Cup hero defeated Spanish lucky loser Albert Ramos 6-2 7-6 (7-5) in his second-round match.

But forget Stepanek – Del Potro’s biggest concern is surviving the Australian summer without breaking his trusty Wilson Pro Staff 2012, which is out of stock – even for the world No.5.

Del Potro has been trying out a series of new weapons during the off-season without any joy and, wary of Roger Federer’s troubles last season adjusting to his bigger-framed Wilson, the big Argentine is reluctant to change on the eve of a major.

“It’s not easy to change racquet,” del Potro said.

“I mean, the racquet is our life. If I don’t feel good with my racquet, my game could be changed a lot.

“I’m very specific with my details of the racquets.

“You can see what’s happen with Roger last year. He try to change and he lost confidence with his game.

“And also, we don’t have too much time to try racquets, to change, because every tournament are very important for us.

“I mean, if I change the racquet during the off-season, then I came here to play a grand slam and I don’t feel 100 per cent.

“Your mind starts to working in the negative position.”

If he gets past Stepanek, del Potro is likely to meet Russia’s former champion Dmitry Tursunov in the semi-finals.

Fourth-seeded Tursunov beat Czech Lukas Rosol 3-6 6-3 6-3 in his second-round match on Wednesday.

Australian wildcard Marinko Matosevic continued his breakthrough summer with a second-round upset win over third seed Andreas Seppi.

Matosevic, the world No.56, thrilled fans under grey skies at Sydney Olympic Park with a 6-3 6-4 victory over the 25th-ranked Seppi.

Matosevic had never won a main-draw match in Australia before this summer but is now through to back-to-back quarter-finals after also reaching the last eight at the Brisbane International.

After falling to Federer in Brisbane, Matosevic has a much more inviting opportunity on Thursday against Ukraine qualifier Sergiy Stakhovsky to make the last four.

Fellow Australian Bernard Tomic will be looking to join Matosevic in the quarter-finals later on Wednesday when he continues his title defence against Slovenian qualifier Blaz Kavcic.