The big-spending Chinese club had imposed an internal suspension on their Argentine star, but lifted that for Tuesday's vital win where he was the hero guiding them to the last 16
Conca had been handed a nine-game club-imposed suspension last week for his reaction to being substituted after an hour in the matchday five 3-1 defeat to Jeonbuk Motors, where he later criticised the coach on Weibo, the Chinese equivalent of Twitter.
The Argentine had flown to Thailand with the squad, although Lee said on Monday he wouldn't play, however Conca started and provided a second-half assist before netting the vital 90th-minute winner from the spot.
"We had to penalise him (Conca) for his misconduct but we also had to include him on the roster as he is a crucial part of our team," Lee told reporters after the game.
The result sees big-spending Guangzhou top their group, allowing them home advantage in their Round of 16 clash against either FC Tokyo or Ulsan Hyundai.
Ambitious Guangzhou are also the final Chinese side alive in this season's competition and Lee said they were now representing their country on a "new adventure".
"Guangzhou are now representing the whole of China, not just Guangzhou, so I'm extremely happy to have been able to grab this win against Buriram United," the Korean coach said.
"In Group H it has been quite tough because all of the teams have been so competitive, so we are thankful for all the fans and supporters back in China and those here in Thailand.
"Starting from this moment, we are beginning a new adventure, fighting our way into the Round of 16."