Mark Cavendish sprinted to a spectacular victory, a record eighth Tour of Britain stage win, in North Wales as Sir Bradley Wiggins retained the race lead.
Wiggins came in safely in 22nd on the same time as Cavendish, as Sky pulled back an eleven rider break in the final kilometre to set up a bunch sprint.
With the race all back together, Cavendish could head home Stage One victor Elia Viviani and Steele Von Hoff on the shores of Llyn Padarn, for his eighth win in his home Tour.
"It's always nice to win here,” said the Omega Pharma Quick-Step rider afterwards. "It's always nice to win in front of your home crowd and I've got a good relationship with the organisers. I've seen this race grow over the last ten years, you've only got to look at the crowds in the last couple of years, it makes you proud.
"To be able to do it in this jersey that represents the champion of the country. I'm very proud and very patriotic, so it's an honour for me,” said the Manxman who is the reigning British Road Race Champion.
An 11 rider break had gone clear racing through Loggerheads, including the SKODA King of the Mountains jersey of Angel Madrazo and Aaron Gate of AN Post Chain Reaction, who moved back into the Yodel Direct Sprints Jersey at the end of the day.
With Sky Pro Cycling monitoring the advantage and keeping it below the four minute mark the break was always in danger of being brought back.
A lead of over a minute at the foot of the final SKODA King of the Mountains climb of Pen-y-Pass with just over ten kilometres of racing was annulled, with an attack from Dan Martin prompting a response from the peloton by Nairo Quintana and Wiggins.
The fast run down to the finish in Llanberis saw a fatal hesitation from the leaders, with a brief flurry of attacks from the break failing to stick and no one seeming willing to commit to working.
Heading under the IG sponsored flame rouge the junction was made, with a scrappy sprint ensuing as no one team could take control into the headwind. Cavendish praised Petacchi afterwards for part in leading him through the final kilometre, putting him into a position to head Viviani and Von Hoff at the line.
On the general classification Wiggins remained in the lead, 37 seconds clear of teammate Ian Stannard.
"It was as tough as I thought it was going to be, with the tough weather and the wind,” said Wiggins afterwards. "It always looks different on the tele, but the boys, to keep that gap down to 3:50 all the way, did an incredible job and then if we knew it was going to come back as easy as it did in the last 10, 15k, then perhaps we should have left it a bit more.
"I never look forward to the day after a time trial, the change of bike and stuff. But today I felt good. I'm glad it's out of the way though and we've had another day back on the road bike. Tomorrow's another day though, an important day.
"I think the race will be decided on the two laps. I looked at this stage last week, so it's going to be another tough day tomorrow, probably the toughest really because of that finish circuit.”
TheTour of Britain continues in Wales for Stage Five, a 177-kilometre leg from Machynlleth in Powys to Caerphilly. The stage concludes with two circuits of the SKODA King of the Mountains climb of Caerphilly Mountain, before finishing alongside the world famous castle.
Stage Four, Stoke-on-Trent to Llanberis Brief Results
1) Mark Cavendish, GBR, Omega Pharma Quick-Step
2) Elia Viviani, ITA, Cannondale Pro Cycling
3) Steele Von Hoff, AUS, Garmin Sharp
4) Matteo Pelucchi, ITA, IAM Cycling
5) Jose Joaquin Rojas Gil, SPA, Movistar
6) Owain Doull, GBR, Great Britain
7) Evaldas Siskevicius, LTU, Sojasun
8) Scott Thwaites, GBR, Team NetApp Endura
9) Chris Opie, GBR, Team UK Youth
10) Sam Bennett, IRL, AN Post Chain Reaction
Rouleur Combativity Award, Stage Four: Tom Scully, NZL, Team Raleigh
IG General Classification, post-Stage Four
1) Sir Bradley Wiggins, GBR, Sky Pro Cycling, 16:11:36
2) Ian Stannard, GBR, Sky Pro Cycling, +0.37
3) Martin Elmiger, SUI, IAM Cycling, +0.47
4) Jack Bauer, NZL, Garmin Sharp, + 0.55
5) Alex Dowsett, GBR, Movistar, + 0.57
Chain Reaction Cycles Points Classification, post-Stage Four
1) Elia Viviani, ITA, Cannondale Pro Cycling, 29pts
2) Gerald Ciolek, GER, MTN Qhubeka, 28pts
3) Mark Cavendish, GBR, Omega Pharma Quick-Step, 25pts
SKODA King of the Mountains Classification, post-Stage Four
1) Angel Madrazo, SPA, Movistar, 34pts
2) Anthony Delaplace, FRA, Sojasun, 28pts
3) Mike Northey, NZL, Node4 Giordana Racing, 25pts
Yodel Direct Sprints Classification, post-Stage Four
1) Aaron Gate, NZL, AN Post Chain Reaction, 18pts
2) Angel Madrazo, SPA, Movistar, 16pts
3) Tom Scully, NZL, Team Raleigh, 13pts
Under-23 Classification, post-Stage Four
1) Simon Yates, GBR, Great Britain, 16:12:59
2) Jacob Rathe, AUS, Garmin Sharp, + 0.41
3) Alistair Slater, GBR, Great Britain, + 0.52
Team Classification, post-Stage Four
1) Sky Pro Cycling, 48:36:43
2) IAM Cycling, + 2:03
3) Movistar, + 2.11