"They wrenched the jaws of the clamp ... I was devastated," the 68-year-old said.
He reported it to the police and started making plans to get a back-up bike so he could still race today.
Just by chance, the couple called into AvantiPlus Pedal Power in Taradale on Friday so Mr Winstanley could have a look at what he might replace his stolen bike with.
He was telling staff about the theft when one piped up about an email police had sent querying the make of a bike they suspected was stolen.
Owner Stephen Humphreys showed Mr Winstanley the bike. He confirmed it was his.
Mr Humphreys, a former police officer, got on the phone to constable Ben Dalton saying he knew who the bike belonged to and that yes, it had been stolen.
The call from Mr Humphreys gave police sufficient evidence to get a warrant and recover the bike from a Napier property, the Tactical Crime Unit officer said.
One person was being spoken to in relation to the matter.
Mr Dalton said thieves were active at this time of year so people needed to take extra care.
Mr Dalton said people have to be "very aware" of buying items off Facebook selling sites.
"There is a large amount of stolen property on there and people buying items run the risk of being charged with receiving."
Mr Dalton was pleased that Mr Winstanley would be able to ride his own bike in the race.
Mr Winstanley was grateful to have one of his three bikes back.
"To replace it was going to cost me a lot of money, being a pensioner."
He will ride 160km on his bike today.