However, the Dundalk woman immediately showed she remained in the form of her life by setting a new 60m hurdles personal best of 8.30 seconds.
A high jump of 1.81m – only three centimetres down on the best she set in the Netherlands – was followed by another lifetime best shot put of 14.64m, which added 10 centimetres to her previous best mark.
That left O’Connor, who won Commonwealth Games heptathlon silver for Northern Ireland behind Katarina Johnson-Thompson in 2022, in second place after three events.
While she slipped to third – just three points behind US athlete Taliyah Brooks – despite another long jump personal best of 6.32m, the Northern Ireland athlete finished well ahead of the American in the concluding 800m to secure the silver.
“I knew that to get the silver, I had to beat the American girl, so that was just the plan. I just wanted to go out and run hard and just fight until the very end,” she added.
“I wasn’t sure where she was at all but for the last 50m I was just thinking ‘how much do you want the silver?’ I’m upgrading from [bronze at the] Europeans so I’m really happy.”
O’Connor also told Athletics Ireland she hopes her medals over the last fortnight will “really push multi-events forward in the country and let younger athletes see what other options are available to them in athletics”.
She becomes only the seventh Irish athlete to claim an individual medal at a World Indoor Championship, following in the footsteps of Marcus O’Sullivan, Paul Donovan, Frank O’Mara, Sonia O’Sullivan, Paul McKee and O’Rourke.