The Sky Academy Sports Scholar had already secured the 200m freestyle title and a silver in the 100m butterfly on Thursday and was one of the favourites to medal in her favoured 200IM.
O'Connor more than lived up to the pre-race expectations as she led from the start to win in an a new English record time of 2:09.71 - the second fastest time this year.
It meant she was comfortably under the Commonwealth Games consideration time and left a high quality field trailing in her wake. Aimee Willmott took the silver as she touched home almost a second behind with Sophie Allen, O'Connor's Bath team-mate, taking the bronze ahead of former champion Hannah Miley.
“I’m very happy with my win. The 200 medley is my favourite event and I’m thrilled to have set a new English record and got under the consideration time," said O'Connor.
“I felt good during the first 100m but it’s such a strong field that I knew they would come back if I didn’t push myself. I didn’t have a lot left in the last 25m but I dug really deep and am really happy with the time.”