The cursed seal isn't used for suppressing chakra. The CS forcibly draws out chakra. No one really knows the deal between Anko's encounter with Oro. All we know is that Oro activated the CS on her back and then she went down in pain. I would be willing to say that Anko's CS was experimental.
Whatever the case may be, he was able to bring her to her knees without any visible effort because of the Seal.
"For I being a poor man, have only my dreams & I have spread them beneath your feet. Tread carefully, for you tread upon my dreams."