Socceroos coach Holger Osieck has been quick to warn that the serious business is still to come in the wake of Australia's 2-1 triumph over South Korea.While Australia's impressive showing against a fellow Asian heavyweight is cause for celebration, the German's sights remain set on securing the Socceroos their third straight World Cup berth."I think we have to be realistic," Osieck said."Today it was a friendly game and the qualifying games are a lot more difficult, that's for sure."Now we have four more (World Cup qualifying) games, three games in Australia and, of course, we have to prepare for each game according to the opponent."We know all the teams now and I think I will find the right means to be successful."Nikita Rukavytsya and Robert Cornthwaite scored their first international goals as an experimental Socceroos ground out their 2-1 win.In a match where exciting youngsters Tom Rogic, Aziz Behich, Eli Babalj and Mathew Leckie were all handed debuts off the bench, fringe players Rukavytsya and Cornthwaite made the most of rare starts to secure a come-from-behind win.Striker Rukavystya's first goal in 10 appearances, set up by Tommy Oar, cancelled out Lee Dong-Gook's 12th minute opener after the Socceroos had been dominated early by their Asian rivals.But Australia improved after halftime, with Cornthwaite tapping home the winner in only his second appearance in the 88th minute after Babalj had struck the woodwork.The performances of several Socceroo newcomers will almost certainly create future selection headaches for Osieck, who was particularly impressed with Cornthwaite."Robert Cornthwaite, he came into the team because we had two defenders injured and he played very well tonight and I'm very pleased by his performance," Osieck said."He definitely will be a future member of our team."Against a youthful South Korean line-up that featured only three players with 10 or more caps, each of Osieck's young guns showcased the options available to the Socceroos ahead of their crucial World Cup qualifiers."I think both teams played a very good game and speaking for my team, I'm very pleased with the performance of these young guys," Osieck said."They showed some really promising elements and I hope I can build for the future with these players."Skipper Lucas Neill was equally impressed by the application shown by his new teammates."The attitude has been very good and there's definitely talent in the squad," Neill said."Great credit to the guys, they didn't come out and show too much nerve."A little bit of a slow start, but when we got going everyone took their opportunity."In the end we got what I felt was just rewards."