VIENNA  - Australian Marinko Matosevic produced the shock of the first day of the ATP Austrian Open here on Monday as he beat Dutch sixth seed Robin Haase 1-6, 6-3, 6-2.

Matosevic's world ranking of 55 is the best of his career and the 27-year-old Aussie showed he means to hold onto it in his victory featuring five aces and four breaks of serve in 97 minutes. Gilles Muller of Luxembourg staged a fightback to overcome Belgium's Steve Darcis 6-7 (3/7), 6-4, 6-3 with the winner firing down 16 aces but needing almost two and a half hours to advance.

Argentine Juan Martin del Potro, the top seed, is making a re-appearance after a month out with a left wrist injury, last playing in a Davis Cup semi-final loss to the Czech Republic in Buenos Aires. The Argentine is fighting this week for one of three remaining spots at the World Tour Finals which wrap up the season from November 5 in London.

Del Potro lost the Vienna final last year to Jo-Wilfried Tsonga and will hope to go a step further this week to help his cause. The provisional number seven in the London field is expected to duel with number nine rival Janko Tipsarevic, also in with a chance and seeded two here. Spain's David Ferrer on Monday claimed the fifth place behind Roger Federer, Novak Djokovic, Andy Murray and the injured Rafael Nadal.