The German coach was understandably frustrated to have lost the three points so late in the game but was delighted by the maturity and tactical astuteness shown by his players
The German champions turned in an impressive performance but were denied an invaluable three points when Mario Balotelli's last-gasp spot kick cancelled out Marco Reus' strike.
In his post-match conference, the former Mainz coach expressed his disappointment at failing to hold on to the lead but feels that his side are showing signs of real progress in this year's competition.
"I am a little bit annoyed about this result, even though City deserved a draw as well. You cannot keep out the incredible talent of Manchester City for 90 minutes," he said.
"We had them pinned down, so of course you'd like to take the three points in that case. We had countless chances, despite being the away team.
"However, we can build on this performance, as we were very disciplined tactically. It was a big step forward for us."
Dortmund have gained four points from their opening two matches but face a stern test when they host Real Madrid on Wednesday, October 24.
Last season, they finished bottom of their group and Klopp will be hoping to reach the knockout stages this time around.