Australia's Sam Welsford claimed his second stage win on the back of a slick Bora-Hansgrohe team performance as Isaac Del Toro Romero clung on to the overall lead halfway through Australia's Tour Down Under on Thursday.

Welsford, who won Tuesday's first stage in the WorldTour season opener, took full advantage of another supreme lead-out from his teammates to finish just ahead of Italy's Elia Viviani in a frantic finish in Campbelltown.

But young Mexican Del Toro Romero (UAE Team Emirates) held on to the leader's ochre jersey by two seconds from New Zealand's Corbin Strong (Israel-Premier Tech), with Frenchman Axel Mariault (Cofidis) moving into third five seconds off the lead. Welsford was 72nd overall 50 seconds down.

"To get one, let alone two is really special, and these guys are just amazing," Welsford said.

"Full commitment down the gorge. It's just super nice that they have that belief in you. It's an incredible ride and I'm riding the wave."

Welsford was perfectly positioned behind his team on the fast and hair-raising descent into Campbelltown.

The German Bora-Hansgrohe team occupied the top third of the peloton and patiently waited for their chance to hit the front with three kilometres to the finish.

In the final 300 metres, Danny Van Poppel took Welsford to top speed before swinging off, leaving the 27-year-old Australian to power on and hold off the fast-finishing Viviani (Ineos Grenadiers) by a half bike length.

While Welsford dominated the headlines in the 145.3-kilometre third stage, Del Toro Romero finished safely in the bunch finish, coming in 33rd and credited with the same time as Welsford.

Viviani, a nine-time Grand Tour stage winner, grabbed his first podium of the new season, and narrowly missed out on adding to his TDU stage wins in 2018 and 2019.

Leading home hope Luke Plapp (Jayco-AlUla) crashed heavily on the road surface with about 10 kilometres to go on the fast downhill run toward the line but managed to climb back on his bike and complete the stage.

He looked a forlorn sight as he limped across the line with his kit ripped to shreds, revealing extensive patches of grazed and bloodied skin on his shoulder and back.

His Jayco-AlUla team said: "Not the ideal day with a very unfortunate fast crash for Australian champion Plapp in the final 10km. He managed to finish the stage but with lots of skin lost."

Three Astana riders --- Christian Scaroni, Samuele Battistella and Michele Gazzoli -- were also involved in the high-speed crash and finished the stage. They will all be medically assessed before Friday's fourth stage.