Richie Porte has won the Tour Down Under for the second time, but had to settle for the runner-up's place on the final gruelling stage to the top of Willunga Hill.

Key points: Richie Porte won his first Tour Down Under since 2017

Richie Porte won his first Tour Down Under since 2017 Porte was chasing a seventh victory atop Willunga Hill but was beaten up the climb by British rider Matthew Holmes

Porte was chasing a seventh victory atop Willunga Hill but was beaten up the climb by British rider Matthew Holmes The leader heading into the final stage, Daryl Impey, faded on the final climb

The Tasmanian finished second behind unheralded Englishman Matthew Holmes on a stage he has won for the last six years, after a mass breakaway on the 151.5-kilometre final stage threw the overall race standings into turmoil.

Two-time defending champion Daryl Impey of South Africa entered the last stage with a two-second lead over Porte on general classification in the first World Tour event of the season.

But Impey's chances of an unprecedented third-straight win dissolved on the second of two climbs up Willunga Hill while Porte launched his trademark attack on the second climb to put the overall result beyond doubt.

However, Porte's chance of extending his unprecedented winning streak on the Willunga stage was lost when Holmes, riding a World Tour event for the first time, swept past him over the crown of the hill and beat him to the finish line by three seconds.

Loading

The 26-year-old from Wigan in north-west England was part of a 26-rider break which sowed panic among teams whose riders were in contention for the win.

The breakaway maintained a lead of more than four minutes over the peloton until the first of the two climbs up Willunga Hill.

With so many riders in the break, including leading riders such as Andre Greipel, the peloton was fully stretched to close the gap. At one point young American Joey Rosskopf, who started the day 58 seconds behind Impey on general classification and was in the leading group, held a virtual lead of more than three and a half minutes on the road.

Porte's teammate, world road champion Mads Petersen, did a superb job of leading the peloton's chase for the breakaway and it was through his efforts that Porte was able to finally launch his winning attack on the second climb.

The break began to fall apart on the first climb up Willunga Hill and completely broke up on the second as Porte drove to the front of the race. Impey couldn't go with him and dropped back to finish 30 seconds behind Porte in fifth place.

"It was a little bit panic stations there in the middle [of the stage]," Porte said.

"We had to do the ride for the whole day.

"My team today were absolutely fantastic. It's been an incredible week.

"People are quick to single out Mads Petersen because he's the world champion and he's there helping me. But everyone's been incredible."

Porte also paid credit to women's Tour Down Under champion Ruth Winder, who rides in Porte's Trek Segafredo women's team.

Loading

"It's fantastic and for our team to also win the women's tour, it's a great start to the year for us."

Holmes was able to hang on when the break fell apart to challenge and eventually out-sprint Porte.

"There's no way I thought I would win that in such a big group," Holmes said. "I've never really raced up a climb. I've been stuck in Britain for the last six years.

"This is my second hilltop finish this week. They seem to suit me."

AAP