Defending champion Juan Martin del Potro suffered a stunning defeat from the hands of Kazakh qualifier Mikhail Kukushkin in the quarterfinals of the Apia International Sydney.

The Argentine giant, who returned to action after a 10-month layoff from a wrist injury, squandered two tie-breakers in as many sets to go down 6-7 6-7 at the Ken Rosewall Arena on Thursday.

Moving on, Del Potro will look to better his form at the Australian Open 2015 in Melbourne that begins from January 19.

QUARTERFINAL RESULTS – SINGLES

(Q) M Kukushkin d. JMD Potro (7-6, 7-6)

(5) L Mayer d. (4) J Benneteau (6-3, 7-6)

G Muller d. Bernard Tomic (7-6, 7-6)

(Q) V Troicki d. S Bolelli (6-3, 3-6, 7-5)

QUARTERFINAL RESULTS – DOUBLES

R Lindstedt/M Matkowski d. (4) A Qureshi/N Zimonjic (6-4, 6-3)

(Image: dailytelegraph.com.au)