That's all from me today. Thanks for your tweets and company. I'm back on Friday to take you through the weekend's action.

Paul Fletcher will be in the chair for Wednesday's stage. Be sure to join him.

It's a 189.5km (117.7 miles) race from Arras to Amiens.

Here's what Geraint Thomas is expecting:

"Barring anything really crazy happening, today will certainly be one for the sprinters. There will be a lot of teams looking to set it up for a bunch sprint, especially if they've not had the chance for one so far. In terms of contenders there's obviously the pure sprinters like Mark Cavendish, Andre Greipel, Alexander Kristoff and Nacer Bouhanni."

Right then, that's stage four done and dusted. the race report is taking shape so it's time to move on to stage five...

Yellow Jersey
Classification

1. Tony Martin (Ger) Etixx - Quick-Step 12hrs 40mins 26secs

2. Chris Froome (GB) Team Sky +12secs

3. Tejay van Garderen (US) BMC Racing +25secs

4. Tony Gallopin (Fra) Lotto +38secs

5. Peter Sagan (Svk) Tinkoff - Saxo +39secs

6. Greg Van Avermaet (Bel) BMC Racing +40secs

7. Rigoberto Uran (Col) Etixx - Quick-Step +46secs

8. Alberto Contador (Spa) Tinkoff - Saxo +48secs

9. Geraint Thomas (GB) Team Sky +1min 15secs

10. Zdenek Stybar (Cze) Etixx - Quick-Step +1min 16secs

1. Tony Martin (Ger) Etixx - Quick-Step 5hrs 28mins 58secs

2. John Degenkolb (Ger) Giant +3secs

3. Peter Sagan (Svk) Tinkoff - Saxo

4. Greg Van Avermaet (Bel) BMC Racing

5. Edvald Boasson Hagen (Nor) Team MTN

6. Nacer Bouhanni (Fra) Cofidis

7. Jacopo Guarnieri (Ita) Katusha

8. Tony Gallopin (Fra) Lotto

9. Zdenek Stybar (Cze) Etixx - Quick-Step

10. Bryan Coquard (Fra) Europcar

Jess Parsons: CRACKING end to today's stage on #TDF2015 TT specialist @tonymartin85 takes it! Moments like that are what cycling is all about.

Stuart Mitchell: Sky won't care, they wanted to get through the day, and it's only 12 seconds. Froome will reclaim yellow in a few days.

Andrew Harvey: I'm sweating just sitting at my desk reading the updates! Fantastic effort from @TeamSky and stage winner @tonymartin85! #bbccycling, external

Rob Hayles
Former GB cyclist on BBC Radio 5 live sports extra

"Today shows why Dave Brailsford set the team set up around Chris Froome with a Classics orientated squad. It was particularly for this stage. This was the key one in the opening week where they could have lost significant time but they've come up trumps.

"I'm glad there were no big losses today though because it's kept everyone in the chase, the top four in particular. It's shaping up to be an incredible race."

I must admit to missing that bit. I saw Martin suffer a problem with around 20km remaining. It appears as though he got on Matteo Trentin's bike and rode to the finish on that.

And for those of you wondering why Team Sky and Chris Froome will be happy to be rid of the yellow jersey - it's mainly to do with the pressure of holding it. They will now be able to relax over the next few days and worry about winning it back when they hit the Pyrenees next week.

Here's Tony Martin's thoughts on that finish: "After having a flat tyre and changing bikes I was thinking about the next stage. But I got back in and with 5km remaining everybody was looking round and not pulling so I went for it. A thousand thanks for my team. I am super happy."

Big hugs and kisses all round in the Etixx - Quick-Step team. It's been an eventful few days for Mark Cavendish and his team-mates. After messing up the sprint on stage two, they got it so, so right today.

Martin's German team-mate John Degenkolb was second over the line, one second adrift, with Peter Sagan third and Greg van Avermaert fourth.

Rob Hayles
Former GB cyclist on BBC Radio 5 live sports extra

"What an incredible finale for Tony Martin. He has just missed out on the first three stages. He deserves it so much. He started out just one second behind Chris Froome and Team Sky will not be bothered to lose the yellow jersey."

Yellow Jersey
Classification

Image source, AP

Tony Martin wins stage four and takes the yellow jersey.

Martin is into the final 200m, he's going to win this and ride into the yellow jersey...

Mark Cavendish is hovering in the train, about eighth wheel. He does not need to worry about a leadout because his team-mate Martin is going for a solo victory. But Martin is only five seconds clear as he enters the final kilometre.

Tony Martin is a three-time time trial world champion so he is used to putting in a big effort and holding on. He has 2km to go. If he wins, he is in the yellow jersey.

Rob Hayles
Former GB cyclist on BBC Radio 5 live sports extra

"I don't think Team Sky will be chasing. They won't mind if they lose the yellow jersey today."

There are two right-angled bends in the final kilometre and the last 600m is uphill. Doesn't sound perfect for Cav, who prefers the flatter sprint.

And while everyone is looking at each other, Tony Martin goes on the attack.

Rob Hayles
Former GB cyclist on BBC Radio 5 live sports extra

Image source, AFP

"Mark Cavendish is in this lead group. On this finish if he's got the legs, he could be getting his hands in the air. But his Etixx - Quick-Step team have got Tony Martin to think about as well."

We are 5km from the finish and all the big favourites are in the mix. As exciting as the cobbles have been, they've not been quite as divisive as last year.

I don't think any of the big four will be looking for a stage win. So it's down to the likes of Sagan, Degenkolb, Van Avermaert etc...who's your money on?

Geraint Thomas and Chris Froome are back on the front of the bunch. I want what G has for breakfast.