Victory for Lotto-Soudal's Greipel is his second of the race, having sprinted to victory on stage one. It also takes his total of number of stage wins in the Australian race to a record 18.
The German beat Caleb Ewan (Mitchelton-Scott) on the line in the centre of Adelaide, with Peter Sagan (Bora-Hansgrohe) third. Impey finished safely to secure the final Ochre jersey.
Despite finishing on the same time as Richie Porte (BMC Racing), Impey's triumph comes courtesy of three second-placed finishes in the race. It is his first general classification victory since he won the Tour of Alberta in the Canadian Rockies in 2014. His only other overall stage racing success was the Tour of Turkey nine years ago.
Two stage wins for Greipel is the perfect start to his season and immediately stores away the horrors of 2017, when he only managed five wins.
How it unfolded
The sixth and final stage of the opening WorldTour stage race of the season was a traditional 90km criterium in downtown Adelaide comprising of 20 laps of a city centre circuit.
Two breaks formed in the first three laps, the first bigger than the second, but both failed to stick. AG2R La Mondiale's Mikael Cherel jumped away from a regrouped peloton on lap four, and he was chased down by Koen de Kort (Trek-Segafredo) and Manuele Boaro (Bahrain-Merida). That break, too, wasn't allowed to stay away.
On lap five, the break finally stayed away. Education First-Drapac's Logan Owen and Astana's Truls Korsaeth weren't judged as too much of a threat and were permitted to stay away, joined not long after by Laurent Didier (Trek-Segafredo).
That break, though, began to fracture, and four laps later only Owen was stay away, accompanied by Dimension Data's Ben O'Connor. The pair maintained a slender lead of around 90 seconds.
With four-and-a-half laps to go, and Lotto-Soudal and Mitchelton-Scott working hard at the front of the peloton to protect their respective interests, Owen opted to go alone. His lead, however, was brought to an end on lap 18.
The main sprinting teams all took it in turns to lead the peloton through the final two laps, Quick-Step Floors in particular looking strong working for Elia Viviani.
A crash in the final lap didn't upend any of the stage contenders and the peloton were still together as they passed under the flamme rouge.
Viviani was in pole position as the sprints begun with 500m to go. Further back, in 13th wheel, Ewan launched his acceleration, rapidly moving to the right of the road and past the dozen riders who were in front of him.
He powered towards the line and Greipel swung out from the middle to latch onto Ewan's back wheel. With metres running out, Ewan edged his bike towards the finishing line, but Greipel came to the left of the Australian and took victory on the line by half-a-wheel.
Tour Down Under 2018, stage six: Adelaide to Adelaide, 90km
1. André Greipel (Ger) Lotto-Soudal, in 2-01-19
2. Caleb Ewan (Aus) Mitchelton-Scott
3. Peter Sagan (Slo) Bora-Hansgrohe
4. Phil Bauhaus (Ger) Team Sunweb
5. Elia Viviani (Ita) Quick-Step Floors
6. Steele von Hoff (Aus) University of South Australia
7. Simone Consonni (Ita) UAE-Team Emirates
8. Mads Pedersen (Den) Trek-Segafredo
9. Carlos Barbero (Esp) Movistar
10. Mads Würtz Schmidt (Den) Katusha-Alpecin, all at same time
Final general classification after stage six:
1. Daryl Impey (RSA) Mitchelton-Scott, in 20-03-34
2. Richie Porte (Aus) BMC Racing, in same time
3. Tom-Jelte Slagter (Ned) Dimension Data, at 16 secs
4. Diego Ulissi (Ita) UAE-Team Emirates, at 20 secs
5. Dries Devenyns (Bel) Quick-Step Floors
6. Egan Bernal (Col) Team Sky
7. Gorka Izagirre (Esp) Bahrain-Merida, all at same time
8. Luis Leon Sanchez (Esp) Astana, at 23 secs
9. Ruben Guerreiro (Por) Trek-Segafredo, at same time
10. Robert Gesink (Ned) LottoNL-Jumbo, at 24 secs
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