Argentina coach Diego Maradona admitted his side will face greater tests after their 2-0 victory over Greece at the Peter Mokaba Stadium made it three wins in succession in Group B.
Defender Martin Demichelis and substitute Martin Palermo scored the goals in the last 13 minutes after finally breaking through a determined Greek rearguard action.
Bayern Munich centre-back Demichelis fired home from close range in the 77th minute after his header from Lionel Messi's corner bounced back off team-mate Diego Milito.
Boca Juniors striker Palermo tapped in the rebound from Messi's shot to complete the victory a minute from time.
"Now the road gets more difficult," said Maradona.
"You always hear about Germany, Italy, Brazil playing poorly, but they're always in the second round, quarters, semi-finals and the final."
With his side virtually qualified even before they played their final match Maradona made seven changes but insisted on playing Messi and in the process he made the Barcelona forward Argentina's youngest captain two days short of his 23rd birthday.
"It was a unique experience - something very special," said Messi.
"As soon as I knew about it it was just great, unique."
Meanwhile, the 36-year-old Palermo - the least heralded of Argentina's much-celebrated strikeforce - was delighted to have repaid Maradona's faith with a goal.
"This is priceless," said the Boca Juniors forward, who is behind Gonzalo Higuain, Diego Milito, Carlos Tevez and Sergio Aguero in the forwards pecking order. "I will always be grateful to Diego Maradona and to the staff for their confidence in me, knowing there are others ahead of me.
"My team-mates celebrated with me as if they had scored themselves."
Maradona also rounded on his critics, who were many when Argentina stumbled through qualifying and made it only with two wins in their last two matches.
"They (the critics) should apologise to the players, who are 100% professional," said the World Cup winner.
"We are doing our duty, which is to defend the Argentina shirt. Sometimes they are wrong, but those who have also criticised are wrong and should apologise."
The coach was also unimpressed by some strong-arm tactics in trying to keep Messi quiet, which Greece achieved until the last 10 minutes of the game.
"Where is the famous fair play? If every time Lionel Messi gets the ball he is thrown to the ground, what are we talking about?" he added.
"They should get a yellow card to stop it, because that is in the rules."
Greece coach Otto Rehhagel admitted his side were second-best.
"It was a well-deserved victory, no doubt about that," said the 71-year-old German, whose side lost out on second place after South Korea drew with Nigeria.
"We wanted to avoid an early goal, we managed to do that, but of course Argentina has more class and that earned them the win."
"My players played with their hearts and with excitement
"But it was just not enough to cause Argentina much trouble."