Ulster's unbeaten start to the GUINNESS PRO12 season was left in tatters at Stadio XXV Aprile while Zebre got off the mark with a gritty 13-6 victory.
Dario Chistolini crossed in the second half - Kelly Haimona adding eight points with the boot - as the Irish province never recovered from prop Declan Fitzpatrick's early dismissal.
But Doak says Ulster, who will look to respond at home to Edinburgh on Friday, should be prepared for any setback that comes their way.
"We didn't really control areas of the game that we should have controlled and unfortunately we came away on the wrong side of the game," Doak told the Belfast Telegraph.
"The set-piece was always going to be a bit of a struggle when you lose a prop.
"We talked about it before, ironically what happens if cards come about and unfortunately for us it did come about and we weren't able to cope.
"We just didn't control areas we should have and that was our downfall."
Click here for the best images from Zebre's victory over Ulster.
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