Del Potro vows to atone for another early departure

Juan Martin del Potro promised to keep working for an elusive second Grand Slam title after yet another chance slipped through his fingers at the Australian Open.

Expectations are habitually high for the towering world No 5 and optimism rose anew when he thumped Bernard Tomic in last week's Sydney International final.

But the 2009 US Open champion struggled in Melbourne and he was taken to four sets by qualifier Rhyne Williams in the first round, before crashing out to Spain's Roberto Agut Bautista in the second.