For the second consecutive stage young legs finished fastest as Stewart just edged out his New Zealand track endurance squad-mate Corbin Strong and previous tour leader Jensen Plowright on the Te Anau lakefront finish line.
Time bonuses enabled Stewart, who claimed his first senior rainbow jersey with victory in the gruelling four-event omnium at the world track cycling championships in Poland in March, wrestle yellow from Plowright, along with lead in the under-23 classification.
"It was another solid day out there for everyone. The young guys are really targeting the sprints," Campbell said.
"Everyone was working hard. Our boys were able to bring it back in the last 25km, which was awesome, and it shows that they are on and ready for the rest of the week."
Stewart won four world titles as a junior, along with silver medals in the scratch and points races at last year's Commonwealth Games. He is one of several New Zealand track stars riding in Southland this week.
With World Cups in Hong Kong, Cambridge and Brisbane before next year's world championships and the Tokyo Olympics, the Tour of Southland is considered an ideal endurance-builder for the New Zealand squad.
Stewart is loving the opportunity to step off the boards and into a race he has dreamed of competing in.
"It's pretty awesome. I've watched it on TV for the past four or five years and have always thought it would be something that I wanted to come down and try, and now I've got a yellow jersey on my back," he said.
The 21-year-old will have his work cut out defending the tour lead in the 138km beat from Mossburn to Queenstown which finishes with a 9km, 40min climb towards Coronet Peak.
"[Today] is going to be a hard one. I'm not exactly the best at going up hills, so I'll try and limit the losses and see how it goes."
Yesterday it was another demanding day on the tour. Monday's crosswinds were replaced by persistent rain during the 148km stage from Riverton and over the Blackmount hillclimb to Te Anau.
A group of escapees including James Harvey, Nick White, Jayden Kuijpers, Ollie Jones and Hamish Schreurs and Theo Gilbertson formed the major break of the day.
Jones was the first rider over the Blackmount. But the group's five-minute lead was never going to be enough once the peloton organised a reply.
Stewart has a 4sec advantage over Monday's stage winner Plowright , with Harvey 12sec off the lead and his team-mate and defending champion Michael Vink at 13sec.
Just 15sec separates Stewart, Plowright and Strong in the under-23 classification, while Paul Odlin (PowerNet) contined to strengthen his grip on the over-35 silver jersey.
Jones leads the sprint ace category, while Ioan Fuller is building a handy advantage in the king of the mountain standings.
Leading results after stage 2 yesterday, Riverton-Te Anau (148km).-
Stage: Campbell Stewart (BSR) 3hr 26min 44sec, 1; Corbin Strong (TSF) same time, 2; Jensen Plowright (KAP) st, 3; Ben Oliver (CBW) st, 4; William Green (BSS) st, 5; J-P Van Der Merwe (SSW) st, 6; Antonie Van Noppen (PNL) st, 7; Ruben Eggenberg (VFF) st, 8; Robbie Hucker (KAP) st, 9; Jordan Gilmore (CBW) st, 10 and others.
Overall standings: Stewart 7hr 48min 12sec, 1; Plowright at 04sec, 2; James Harvey (PMK) at 12sec, 3; Michael Vink (PMK) at 13sec, 4; Nick White (KAP) at 13sec, 5; Strong at 15sec, 6; Hamish Schruers (PNL) at 17sec, 7; Hucker at 18sec, 8; Eder Frayre (KAP) at 18sec, 9; Chris Butler (CPB) at 19sec, 10 and others.
