Australian Marinko Matosevic has produced the shock of the first day of the ATP Austrian Open, beating Dutch sixth seed Robin Haase 1-6 6-3 6-2.

Matosevic’s world ranking of No.55 is the best of his career and the 27-year-old will be pushing for the top 50 after his latest win featuring five aces and four service breaks.

Matosevic next plays either Slovakian Lukas Lacko or Austrian Dominic Thiem for a likely quarter-final shot against Argentine top seed Juan Martin del Potro.

In Monday’s only other match, Luxembourg’s Gilles Muller 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.

Del Potro 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 No.7 in the London field is expected to duel with ninth-ranked rival Janko Tipsarevic, also in with a chance and seeded two in Austria.

Spain’s David Ferrer on Monday claimed the fifth place behind Roger Federer, Novak Djokovic, Andy Murray and the injured Rafael Nadal.