Johnson and McClean were at the heart of the action as the Black Cats beat Manchester City 1-0 on Boxing Day, with the former scoring the winning goal.
And O’Neill has identified the two wide men as his team’s main threats, suggesting his side should distribute the ball to them as quickly as possible.
"They can be a threat and this is the whole point,” O’Neill told reporters.
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“With James, we sat here a couple of months ago and we were talking about this second season syndrome, and I was hoping that it genuinely wouldn't be an insurmountable problem for him.
"I knew he would have difficulty early on, and that was shown by the number of times that full-backs went to close him so very quickly in matches.
"He is learning to cope with that now and I am hoping he will overcome it."
The Mackems boss also acknowledged the difficult transition Johnson has undergone since joining the club from Manchester City this summer.
O’Neill added: "Essentially, he was on an excellent run at Middlesbrough, went to Manchester City and by his own admission, he would say he had more cameo roles than anything else, particularly in the last 18 months of his time there.
"To come in here and really be asked to do all the things that we think he's capable of doing, but to change our fortunes, one player changing everything, that was asking a lot.
“He had a wee bit of difficulty early on, but he is overcoming that and he's now starting to show in longer patches, anyway, the sort of form I think he is capable of."