The Tasmanian attacked on the steep final ramps of the final climb of the day of Torrens Hill Road up to Paracombe, making his move with just over 2km to go as Wilco Kelderman (Sunweb) put in a huge dig at the bottom of the climb, dropping a substantial amount of contenders immediately.
None of the key favourites, including Simon Gerrans and Esteban Chaves (Orica-BikeExchange) and Sergio Henao (Team Sky), were able to follow, with Gorka Izaguirre (Movistar) the first to try and match Porte's attack with Chaves just behind.
They were both eventually distanced further as Porte powered out of the saddle up the climb, refusing the cat-and-mouse tactics that panned out on the same stage in last year's edition.
The BMC man has never won the Tour Down Under overall, despite taking victory on the queen stage to Willunga Hill on three occasions, but looked to give himself a huge opportunity at keeping hold of the ochre leader's jersey with the stage two win.
Porte's final gap to Izaguirre and then Chaves saw him take 16 seconds on the line, plus a 10-second time bonus, giving him around a 20-second advantage in GC further time bonuses awarded to second and third place. Porte's teammate, and the 2014 overall winner Rohan Dennis finished in fourth place.
The 148.5km route from Stirling to Paracombe hadn't seen quite the same soaring temperatures that had blighted stage one, but it saw some fierce racing, particularly as the race hit it's final conclusion towards the climb.
Jasha Sütterlin (Movistar) was the lone breakaway rider for the day, getting away with around 20km gone and establishing a maximum gap of five minutes or so.
But there was never much chance of the German holding his advantage, and he saw his valiant effort come to an end as he was pulled back to the bunch shortly before they approached 50km to go.
The main drama came for Team Sky's leading GC rider, Sergio Henao, who suffered an untimely mechanical with just under 30km remaining.
At that point his Sky teammates had been dominant on the front of the bunch as they tried to set things up, but it took a hard chase from several of his teammates, including new climber Kenny Elissonde, to bring him back over a near 15km chase to the bunch.
While the Colombian made it back to the bunch, big efforts from the likes of world champion Peter Sagan (Bora-Hansgrohe) on the approach to the climb took their toll, and Henao was only able to finish 19 seconds back on Porte, nearly half a minute down in GC.
The third stage of the Tour Down Under will see the riders navigate a tricky and hilly course from Glenelg to Victor Harbor over 144km.
Tour Down Under 2017, stage two: Stirling - Paracombe (148.5km)
1. Richie Porte (Aus) BMC Racing, in 3-46-06
2. Gorka Izaguirre (Esp) Movistar, at 16 secs
3. Esteban Chaves (Col) Orica-Scott, st
4. Rohan Dennis (Aus) BMC Racing, at 19 secs
5. Nathan Haas (Aus) Dimension Data
6. Diego Ulissi (Ita) UAE Abu Dhabi
7. Ruben Guerreiro (Por) Trek-Segafredo
8. Michael Storer (Aus) UniSA-Australia
9. Michael Woods (Can) Cannondale-Drapac
10. Luis Leon Sanchez (Esp) Astana, all same time
13. Sergio Henao (Col) Team Sky, st
Overall classification after stage two
1. Richie Porte (Aus) BMC Racing, in 7-10-14
2. Gorka Izaguirre (Esp) Movistar, at 20 secs
3. Esteban Chaves (Col) Orica-Scott, at 22s
4. Jay McCarthy (Aus) Bora-Hansgrohe, at 24s
5. Nathan Haas (Aus) Dimension Data, at 27s
6. Diego Ulissi (Ita) UAE Abu Dhabi, at 29s
7. Nathan Earle (Aus) UniSA-Australia
8. Rohan Dennis (Aus) BMC Racing
9. Luis Leon Sanchez (Esp) Astana
10. Rafael Valls (Esp) Lotto Soudal, all same time
15. Sergio Henao (Col) Team Sky, st
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