Australian champion Ruby Roseman-Gannon was gifted her first World Tour triumph overnight, winning the final stage of the Tour of Britain after a rival threw away the chance of victory by celebrating too early in a bizarre finish.

Roseman-Gannon, the 25-year-old Melbourne star who took both the Criterium and road race titles at the national championships, just couldn't believe it when Luxembourg's Christine Majerus sat up just before the line at the race finish in Leigh, raising her arm in triumph believing she had won.

But it was a calamitous miscalculation as Roseman-Gannon stormed through in the wet conditions in Manchester to pip the Luxembourger to the victory by less than half a wheel, just days after a walker lost her podium place after celebrating early.

"It's when you really don't expect it, some races you come in as a leader and you have a lot of pressure, and other races you come in and it all works out," Roseman-Gannon said.

"Today I was pretty worried about the rain and I was nervous about crashing and I wasn't really in the right mindset that I was going to win the race — but to win is amazing. Overall it was a great race!"

But the final stage proved a bit of an embarrassment to the all-conquering SD Worx-ProTime team as their overall race winner, Lotte Kopecky, tried to "gift" the final stage to her teammate Majerus.

With Belgian world champ Kopecky's overall triumph secured, she eased up with 250 metres left to let Majerus win the day, but the terrible miscalculation let the Australian in.

"We made this deal that she is going to win today but maybe it was a stupid mistake," Kopecky said.

"I still, however, would have done the same. It could have been a nice ending for Christine, but we finished well as a team.

"Maybe it is a little funny and it is what it is, and I'm not disappointed."

AAP