Sunderland will welcome the Swans to Wearside knowing they will have to be at their best to extend their recent record, with Michael Laudrup's men two places and five points better off and having combined their league form with a sensational march into the Capital One Cup final.
O'Neill said: "They just seem to have kicked on. They have done very well. They are coping reasonably comfortably in this league.
"Last season, of course, was one where they were just first time up and not knowing what to expect and they did very well at that time.
"Now they seem to have improved and they have got some very decent players playing for them."