World champion Peter Sagan claimed the race lead at the 2018 Tour Down Under as he sprinted to stage four victory from a reduced bunch in Uraidla.

Hosting a stage finish for the first time, Uraidla didn't disappoint as the late climb of Norton Summit shook up the general classification.

Sagan was one of a number of rouleurs to get over the climb in the 35-strong front group, alongside the GC men, and outsprinted Daryl Impey (Mitchelton-Scott) and Luis Leon Sanchez (Astana) to claim victory.

Peter Sagan, world champion, Tour Down Under, sprint (Pic: Tour Down Under/John Veage)

The world champion will now swap his rainbow bands for the ochre jersey on stage five – which concludes with a double ascent of Willunga Hill – with bonus seconds giving Sagan a two-second lead over Impey.

With searing heat the order of the day again, and temperatures in Adelaide well above the 40-degree mark, only two men braved a day in the breakaway – Zak Dempster and Alex Porter waving the UniSA-Australia flag.

They boasted a lead of nine minutes at one point, with the bunch keen to keep their powder dry, but the chase was timed perfectly.

As the heat from the peloton increased, former Rapha-Condor and Endura man Dempster left his compatriot behind but the fight for position on the run-in to Norton Summit put paid to the breakaway.

With BMC Racing controlling the tempo, race leader – and stage two winner – Caleb Ewan (Mitchelton-Scott) was dropped before they even reached the main climb.

More riders were then shelled out the back as four-time winner Simon Gerrans (BMC Racing) drove a furious pace.

Several attacks failed to make headway on the climb itself, with GC contenders Ion Izagirre (Bahrain-Merida) and George Bennett (LottoNL-Jumbo) among those reined in.

Sagan remained in contention, however, and showed himself on the descent as he attacked from the peloton – forcing a reaction from BMC Racing duo Richie Porte and Rohan Dennis behind.

They successfully chased him down, but after failing to earn a gap with his own attack, Porte could only sit safely in the reduced bunch as the sprint played out.

Willunga Hill is likely to be pivotal again, featuring twice on stage five - the day the race will be all but won or lost (pic: Sirotti)

Impey kicked first, with Sagan on his wheel, but the Slovakian world champion came round him and charged to victory.

With the decisive Willunga Hill stage to come, it leaves Porte, Dennis and a host of other GC contenders in a group of 29 riders sat 14 seconds behind Sagan.

British WorldTour debutant Scott Davies (Dimension Data) is in that group, as is Team Sky new boy Egan Arley Bernal, but it will be all eyes on Porte on Saturday.

Tour Down Under 2018: stage four – result

1) Peter Sagan (SVK) – Bora-hansgrohe – 3.21.07hrs

2) Daryl Impey (RSA) – Mitchelton-Scott – ST

3) Luis Leon Sanchez (ESP) – Astana

4) Diego Ulissi (ITA) – UAE Team Emirates

5) Jay McCarthy (AUS) – Bora-hansgrohe

6) Dries Devenyns (BEL) – QuickStep Floors

7) Domenico Pozzovivo (ITA) – Bahrain-Merida

8) Rui Costa (POR) – UAE Team Emirates

9) Pierre Latour (FRA) – Ag2r-La Mondiale

10) Laurent Didier (LUX) – Trek-Segafredo

General classification

1) Peter Sagan (SVK) – Bora-hansgrohe – 14.19.49hrs

2) Daryl Impey (RSA) – Mitchelton-Scott +2"

3) Jay McCarthy (AUS) – Bora-hansgrohe +9"

4) Luis Leon Sanchez (ESP) – Astana +10"

5) Diego Ulissi (ITA) – UAE Team Emirates +14"

6) Robert Gesink (NED) – LottoNL-Jumbo – ST

7) Rui Costa (POR) – UAE Team Emirates

8) George Bennett (NZL) – LottoNL-Jumbo

9) Dries Devenyns (BEL) – QuickStep Floors

10) Egan Arley Bernal (COL) – Team Sky

Selected others

20) Richie Porte (AUS) – BMC Racing – ST

29) Scott Davies (GBR) – Dimension Data – ST