London, June 15 (IANS) Riding on opener Aaron Finch's big century and a quickfire fifty by Steve Smith, Australia posted an imposing 334/7 against Sri Lanka in their World Cup group stage clash at the Kennington Oval here on Saturday.The defending champions were looking to go past the 350-run mark at one stage but after the dismissals of Finch and Smith, the middle-order failed to capitalise. Skipper Finch, who smashed a brilliant 153 off 132 deliveries (4x15, 6x5), was involved in a crucial 173-run partnership with Smith, who took 59 balls for his 73 (4x7, 6x1).Put into bat, Australia openers David Warner (26 off 48) and Finch started cautiously as their side touched the 50-run mark in 9.3 overs. Dhananjaya de Silva drew the first blood for Sri Lanka as the off-spinner castled Warner in the 17th over, leaving the opponents at 80/1. de Silva struck again 20 runs later, this time packing back new batsman Usman Khawaja cheaply for 10. Finch was then joined by Smith and the duo ensured that Sri Lanka didn't make any further inroads as they repaired the damage, keeping the opponent bowlers at bay.