Highlights - Greece 0-2 Argentina
Argentina coach Diego Maradona has warned his side to expect tougher tests after qualifying from World Cup Group B with a 100% record.
His side beat Greece 2-0 to finish top of the pool and now face Mexico in the knockout round on Sunday.
"Now the road gets more difficult," said the former World Cup winner.
"You always hear about Germany, Italy, Brazil playing poorly, but they're always in the second round, quarters, semi-finals and the final."
Maradona made seven changes to the side that beat South Korea 4-1, resting captain Javier Mascherano, forward Carlos Tevez and hat-trick hero Gonzalo Higuain.
And during the first half Greece, who were dumped out of the competition as a result of the defeat, produced a defensive display that frustrated the new-look Argentina.
It was a unique experience - something very special
Lionel Messi on captaining Argentina
But in the second half, the South American side finally broke the deadlock when Martin Demichelis pounced on a loose ball from a corner, and rifled his shot high into the Greece goal.
Substitute Martin Palermo, 36, made sure of the victory late in the game when he sidefooted past Alexandros Tzoras after the keeper had palmed Lionel Messi's shot into his path.
Messi, who also rattled the post with a fierce strike and forced Tzoras to tip over another effort, was handed the captain's armband for the first time in his international career.
In doing so, he became the country's youngest-ever skipper - two days short of his 23rd birthday.
"It was a unique experience - something very special," said the Barcelona star.
"As soon as I knew about it it was just great, unique."
Maradona paid tribute to 22-year-old playmaker, explaining why he could not rest him.
"We want to be world champions with Messi," added the 49-year-old.
"We had the opportunity to leave him out but we wanted to play him. A lot of people come to see him play. To leave him out would be a sin."
Meanwhile, veteran Palermo was delighted to have repaid the faith that coach Maradona had in him by scoring the second goal.
Palermo has found himself behind Higuain, Diego Milito and Sergio Aguero in the forwards pecking order.
"This is priceless," said the Boca Juniors forward.
"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."