De Jong scored twice in the first 17 minutes to give the Eredivisie side a shock lead over Manchester City at the Etihad Stadium last night [Tuesday].
Yaya Toure and Sergio Aguero eventually drew City level, with the latter denied a late winner to go with Mario Balotelli's unsuccessful penalty appeal.
The result left Ajax third in Group A on four points, four behind leaders Borussia Dortmund and three adrift of second-placed Real Madrid.
Despite that however, De Jong remains hopeful of further surprises as they prepare to face Dortmund and Madrid in their final two matches.
"If you said before the game we'd get four points against City you'd think 'great'," he told UEFA.com.
"We are happy to get four points, now we have to see what we can do in the next two games.
"It's going to be difficult against Dortmund and Real but we have a great feeling about these two matches.
"We are going to hopefully qualify for the next round. Even if we get third in this group with these three other teams it is also a great result but you hope for the best."
Ajax's Danish winger Christian Eriksen believes his team showed beyond doubt they belong in the competition.
"We've proved we know how to play football and we can be on this level," he added.
"We have to keep on - we played very well against Dortmund in the first game but we had no points. Now we have four. To stay in Europe we have to win and that's what we're going to do."