Richie Porte led home a Team Sky one-two as he and team-mate Geraint Thomas lit up Paris-Nice on the Croix de Chaubouret, as Michal Kwiatkowski (Etixx-QuickStep) regained the race lead.
Porte and Thomas continued their hugely impressive start to the season as the Welshman ignited the final climb with a fierce attack inside the final three kilometres before Porte accelerated from further back to pull his team-mate away from a leading trio and take the stage win.
It capped an perfect display on the final climb from Team Sky, who had set the pace from the start through Lars-Petter Nordhaug and Nicolas Roche, and leaves Porte just one second behind Kwiatkowski overall with Thomas a further two seconds back.
Thomas de Gendt (Lotto-Soudal) had earlier attacked almost from the flag, joined by Antoine Duchesne (Europcar) and later Chris Anke Sorensen (Tinkoff-Saxo), to sweep up the King of the Mountains points on the undulating stage.
It was on the eighth and final climb, however, where the race burst into life and Sky took control.
Paolo Tiralongo (Astana) was first to ignite the ascent but Sky’s winter signings Nordhaug and Roche pulled him back and drove the pace on the front.
Race leader Michael Matthews’ resolve cracked with six kilometres still to ride to leave the yellow jersey up for grabs in the front group.
A steady flow of riders continued to drop out the back – Rafal Majka (Tinkoff-Saxo) and Simon Yates (Orica-GreenEDGE) among them – before Thomas accelerated inside the final three kilometres.
Jakob Fuglsang (Astana) responded first and Simon Spilak (Katusha) just about made the junction before Ruben Fernandez (Movistar) and Tejay van Garderen (BMC Racing) jumped out in response.
Fernandez committed the error of watching behind as another counter-attack by Porte followed, however, tumbling and only just avoiding taking van Garderen with him.
As they hit the snow-lined roads with 1500m remaining, the three up front continued to hold a small lead with world champion Kwiatkowski leading the chase behind.
Porte put in a huge dig behind though, catching the front group and passing them with only Thomas able to stick to his wheel.
With the Australian on the front, the two pulled away from the chasing pack to cross in the same time – both punching the air in celebration.
Kwiatkowski finished third to claim enough bonus seconds to take the yellow jersey, but the day belonged to Team Sky.
Paris-Nice 2015: stage four – result
1) Richie Porte (AUS) – Team Sky – 5.18.39hrs
2) Geraint Thomas (GBR) – Team Sky – ST
3) Michal Kwiatkowski (POL) – Etixx-QuickStep +8”
4) Jakob Fuglsang (DEN) – Astana – ST
5) Tejay van Garderen (USA) – BMC Racing +17”
6) Rui Costa (POR) – Lampre-Merida +24”
7) Tony Gallopin (FRA) – Lotto-Soudal – ST
8) Fabio Aru (ITA) – Astana
9) Rafal Valls (ESP) – Lampre-Merida
10) Simon Spilak (SVK) – Katusha
1) Michal Kwiatkowski (POL) – Etixx-QuickStep – 19.44.11hrs
2) Richie Porte (AUS) – Team Sky +1”
3) Geraint Thomas (GBR) – Team Sky +3”
4) Tejay van Garderen (USA) – BMC Racing +27”
5) Jakob Fuglsang (DEN) – Astana +32”
6) Tony Gallopin (FRA) – Lotto-Soudal +38”
7) Rui Costa (POR) – Lampre-Merida +41”
8) Gorka Izagirre (ESP) – Movistar +44”
9) Thiago Machado (POR) – Katusha +50”
10) Rafal Valls (ESP) – Lampre-Merida +51”