Protected all stage, O'Connor and Louis Meintjes were delivered for their soiree up the climb by Ben King and Ryan Gibbons, with eight kilometres to go.
"The group slowly whittled and Ben King was great going back to get some final food to then make Louis and I be in the front.
Left to their own devices, Meintjes struggled and was distanced along with Chris Froome (Sky) and Fabio Aru (UAE) but O'Connor fared better.
"I managed to hold on with the top guys until 900m to go," the 22-year-old said.
"And then after a mini explosion I was able to finish just outside the top 10 in 11th."
"The wind switched and became head/cross which made being opportunistic kind of impossible. Also with the day being so long, today wasn’t just raw numbers – it essentially came down to how well you cope with endurance."
The Aussie now sits in 14th overall.
Dimension Data's Nathaniel Berthane was in the break of the day with 13 other riders, but fell back to the bunch on the final climb.