They take on Switzerland in a Round of 16 clash in Sao Paulo at 5pm.
Inspired by Lionel Messi’s four goals, Argentina topped Group F after three wins in three against Bosnia & Herzgovina, Iran and Nigeria.
Ossie - who played every game as Argentina lifted the trophy on home soil in 1978 - feels there is much more to come.
“We weren’t so good in the first game, not so good again in the second game but much, much better in the third game and if you look at the squad, we have more in the tank,” said our former midfielder and manager, capped 52 times by his country.
“We can go up one or two gears more, that’s the good thing.
“Another good thing is that in the last game it wasn’t just about Messi but Di Maria had a good game, Mascherano and so on.
“I still have the same worries about the defence and that’s not just me, everyone can see that, but it’s looking good.”
Ossie expects a tough game against Switzerland, who recovered from a mauling against Hugo Lloris’ French side - they were 5-0 down before rallying for 5-2 - to finish second in Group E thanks to Xherdan Shaqiri’s hat-trick against Honduras.
“Switzerland started well against Ecuador, lost badly against France, but they still managed to go through and they are a dangerous team,” he added.
“The manager (Ottmar Hitzfeld) has been with the team for a long time, knows the players well and is an accomplished manager so it will be tough, but of course I believe Argentina will go through.
“There are positive signs but one big negative is Aguero’s injury, he’s not going to play and it looks like he’s out for the rest of the tournament. That’s a pity. But I also have a feeling that Messi feels this could be his biggest chance to win the World Cup, so he’s really up for it.”