Guangzhou booked their place with a 3-1 victory over Australia's Central Coast Mariners at the Central Coast Stadium, and Contra says he is very proud of how his side performed in the match.
Contra has not had a long time to prepares his side, having only replaced former England manager Sven-Goran Eriksson at the end of last year.
The Romanian said: "I am very happy for my players because they worked very hard in the last six weeks. I think we deserve to go through to the group stage as in general, we were the better team.
"We scored very fast in the first 10 minutes and I think this changed the game for the opponent also and we had more space for counter-attacks and we had three or four more chances on these counter-attacks, but we didn't score. And after we survived the first 15 minutes of the second half, after the second goal, we had the victory in our hands.
"We scored very fast and this opened the game up, then it was more difficult to attack us as we had more space and we have players who can make very good counter-attacks. We were lucky on some occasions as they pushed very hard in the second half."
The Chinese side booked themselves a spot in Group F, which includes Japan's Gamba Osaka, Seongnam FC from Korea Republic and Thailand's Buriram United.