The attacking midfielder is satisfied with his side's performances so far, and is hopeful of getting a good result against Borussia Dortmund on Wednesday.
The Eredivisie giant was seen as the weakest team in Group D after it was paired with the champions of Spain, Germany and England, yet the team can still qualify for the knockout stages of the competition with two games to play.
"The match against Real Madrid was the only one where we really struggled, but they are one of the best teams in the world," De Jong told Goal.com. "We managed to hold our own in all the other games. We collected four points against Manchester City and we forced them to drop deep on occasions.
"We also got some chances away against Borussia Dortmund. We were unlucky not to get a good result there. It confirms that we are a team to be reckoned with in this group, though."
Ajax hosts Borussia Dortmund at the Amsterdam ArenA on Wednesday, and De Jong is confident the Godenzonen will get their chances again.
"Like I said before, we got our chances in the away game, too. It was a real shame that we conceded the late goal. Things would have been different had we converted one of our chances," he said.
"We play at home now, and will have to play our own game this time around, just like against City. Dortmund are a very strong collective. They always try and attack, but that means we will get chances as well."
Ajax sits third in Group D with four points from as many games, trailing Dortmund by four points.
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