The British rider took the victory in Aldeburgh but crashed just after the finish line and was taken to hospital with a suspected broken leg.
Her Boels Dolmans team had to pick up her jersey and prize at the podium ceremony whilst Armitstead was in hospital.
She was released with nothing broken but will not take any further part in the race which has for its second stage, a stage from Braintree to Clacton.
Armitstead tweeted: "I remember winning with the help of my team mates and then not much else, but I am ok, nothing broken just very sore, thank you for all your kind messages and to the NHS staff who took care of me so well.
"I won't start tomorrow in the hope of recovering properly for the Nationals."
Source: DSG
