Forty riders crashed on a dramatic opening day midway through the windswept 82.6km second stage from Invercargill to Bluff.
Eleven failed to finish the stage.
Roulston avoided the biggest pile-up but had a spill further up the road and was forced out with badly cut knees.
Roulston, a silver medallist at the Beijing Olympics last year, had won the last three tours and was in a good position, with his Colourplus team winning the opening time trial.
But a massive crash involving more than 40 riders on the bridge just through Wallacetown threw the race into chaos.
Officials took the rare step of delaying the race.
With so many bikes lying on the road, the support fleet could not get to the rest of the field.
Stopping the riders proved difficult and in the ensuing confusion, Roulston was caught up in a tangle with leading Subway rider and former tour winner Gordon McCauley.
McCauley had to scramble to find a new bike and while Roulston was able to resume, he pulled out shortly after the restart.
"I ended up in the second crash, just caused by guys not knowing what was going on," Roulston told One News last night.
"I'm not happy with the commissaires.
"I think they made an error today.
"You never see it in Europe.
"When there's a crash there, the race doesn't get stopped."
Tour convener Bruce Ross defended the decision.
"The accident happened within the confines of a bridge so none of the other riders or the support vehicles could get past.
"And for safety reasons, obviously, the commissaires made a ruling in the best interests of the tour to stop the race."
A Southland Hospital duty co-ordinator confirmed two tour cyclists were treated for minor injuries and discharged yesterday afternoon.
Their names were not released.
Little-known Nelson rider Jack Bauer swept past Heath Blackgrove in the last few metres of the climb up Bluff Hill to win the second stage.
Christchurch riders Allan Williams and James McCoy and Australian Samuel Whitmitz had made the race's first decent break.
Struggling into a stiff westerly, the trio opened up a gap along Flora Rd East and stretched their lead to 1min 21sec when the race was stopped. When it resumed, they were caught by a chasing group of four riders and Bauer closed the gap in an impressive display.
All the good work done by Williams and McCoy came to no avail when a strong gust of wind caused them to fall.
Williams pulled out but McCoy was able to resume.
Bauer's powerful ride also looked to be in vain when the bunch came back together with less than 15km remaining.
But, remarkably, he closed the gap on his own again to chase down a group of four riders, including rising star Michael Vink.
Vink powered into the climb and led with 200m to go but Blackgrove and Bauer tracked the 18-year-old and pounced with about 150m remaining.
Bauer stuck to Blackgrove's wheel and went past in the last few metres of the stage.
A frustrated Blackgrove complained he had not been aware the finish line had been shifted around the corner to the left by about 5m and told officials it had cost him the stage win.
Still, Blackgrove can console himself with the yellow jersey for leading the general classification after the first day.
Bauer looked remarkably fresh after the 81.63km stage.
"The winds were coming from everywhere and I thought it was a good idea to stick in the bunch and have a stab at the climb but I got hot feet," he said.
"It paid off in the end because it [the bunch] really split up 10kms out of Bluff and I managed to get across to the lead group at the bottom of the hill."
Bauer said he had struggled up Bluff Hill the last three years but he had been doing a lot of riding in Europe and felt he was in good form.
Today's 165km stage is Invercargill to Gore via Riversdale.
