ADELAIDE (Reuters) - Australia's Richie Porte won his first Tour Down Under on Sunday when he finished behind compatriot Caleb Ewan in a bunch sprint on the final 90-kilometre sixth stage around the streets of Adelaide.

Orica-Scott's Ewan outsprinted world champion Peter Sagan to clinch his fourth stage on this year's Tour, joining Germany's Andre Greipel (2028) and Australia's Robbie McEwen (2002) as the only riders to have won four stages in the same race.

The 31-year-old Porte, who had finished second in the race the last two years, was 48 seconds ahead of Colombian climber Esteban Chavas, with Australia's Jay McCarthy given third overall, three seconds further back.

Nathan Haas, who had started the final stage in third, was credited with the same time as McCarthy, who took the podium on countback.

Porte, who broke his shoulder in a crash during the Rio Olympics road race, said having a break after the Games had been key to him claiming his first Tour Down Under title.

"After crashing in Rio and injuring myself in a nasty crash, it wasn't too hard to motivate myself for this race," Porte told reporters. "I had a good break and I came here fresh, physically and mentally.

"It's incredible to come back here and win ... after being so close in the last two years.

"I owe each day of racing successfully here to my team mates. They took me to the line every day and it's a massive credit to them. It was a dream for me to win this race."

BMC's Porte had extended his lead to 48 seconds when he won the 151.5 kilometer fifth stage from McLaren Vale to the summit of Willunga Hill on Saturday.

While essentially a procession for Porte's victory, the final stage, which comprised 20 laps on central Adelaide streets, featured an early breakaway by Belgium's Tomas De Gendt and Italy's Gianluca Brambilla, who established a 30-second lead before they were hauled in.

Seven others managed to get away from the peloton about halfway through the stage, establishing a 58-second gap and held on until the penultimate lap when the last of the seven -- New Zealand's Jack Bauer -- was reeled in for a final bunch sprint.

The six-stage race around South Australia is the first event on the 2017 UCI WorldTour calendar.

(Writing by Greg Stutchbury in Wellington; Editing by Peter Rutherford)