ADELAIDE - South Africa's Daryl Impey surprised even himself when he won the UCI season-opening Tour Down Under on the streets of Adelaide on Sunday.

Impey secured the biggest win of his career when he finished safely in the peloton behind stage winner Andre Greipel, who beat Impey's Mitchelton-SCOTT teammate Caleb Ewan with a lunge to the finish line. Impey went into Sunday's final stage on the same time as pre-race favourite Richie Porte but ahead of the Tasmanian on a count back.

All he needed to do to secure the overall win was to finish safely, an outcome that appeared never to be in doubt on the 90-kilometre stage on the Adelaide street circuit. Impey came into the race as the final lead-out rider for Ewan and was never expected to challenge for general classification.

But his determined ride up Willunga Hill to finish second to Porte in Saturday's penultimate stage was enough to place him level on time with Porte and ahead on a count back because of his superior finishing positions in the earlier stages. "Coming into the race I didn't expect to win it but sometimes the stars line up and everything goes well," he said. "I worked really hard in the off-season so I'm happy to get this win."

Impey said the final stage, 20 laps of a 4.5-kilometre street circuit, had been "pretty hectic" as a number of riders battled to improve their overall finishing positions. "I've been in this position before with Simon (Gerrans), trying to protect the jersey for him, but it's definitely more nerve-wracking when you've got the jersey yourself," he said.

The 33-year-old won a stage of the Tour De France and wore the yellow jersey for two stages in 2013. He won the 2009 Tour of Turkey and the 2014 Tour of Alberta but Sunday's win was his first on the World Tour.

He said the win, combined with Nicholas Dlamini's effort in taking the King of the Mountain title, was a boost for South African cycling. "There's a lot more to expect from South Africans," he said. "I mean Nick Dlamini in his first race, the whole of South Africa can be proud of him."

Sunday's stage took on a familiar feel as small groups of riders tried to break away and go for individual glory. But every attack was reeled in and by lap 19 the race was all together as the teams came forward to try to put their sprinters in the best position.

On the tight circuit the race became disorganised and many of the sprinters were left on their own. Elia Viviani went early but he was caught by Ewan and Peter Sagan, with Ewan powering clear only to be caught by a lunging Greipel on the line, the German winning his second stage of the race and his 18th overall.