Ahead of today's opening practice session the air temperature is 27 degrees C, whilst the track temperature is 44 degrees.

Tyres available this weekend are soft and supersoft, a step down on last year's medium and soft.

There are two DRS zones. The detection point for the first is 40m before T7 with activation 390m after T7, whilst the second detection point is 50m after T9 with activation at T10.

Having missed the last two races Caterham returns to the grid, thanks to the success of its crowd funding project, with Kamui Kobayashi joined by British rookie Will Stevens.

There are two test drivers in action today, Esteban Ocon replacing Grosjean at Lotus and Adderley Fong replacing Sutil at Sauber.

The lights go green and so begins possibly the most important weekend of the F1 year, not just for the two title combatants but those drivers (and teams) still unsure of the future, unclear as to whether this is their last race or not.

First out is Perez, followed by Kobayashi, Bottas, Vergne and Gutierrez.

Returning to his garage Gutierrez slides to a halt and clops a couple of mechanics in the process.

Five minutes into the session all but the Red Bulls have been out.

Even though the teams are testing here next week a number of cars are sporting sensors. Magnussen is one of the drivers running with sensors, the Dane trying a new front wing courtesy of former Red Bull designer Peter Prodromou. Elsewhere, teammate Capt. No Grip complains of "very low grip" in the pitlane.

Ten minutes into the session and there is nobody - nobody - on track. Then again, this has become the norm here as no other session is held this early in the day. (13:00 local time).

Eventually Maldonado, Kvyat, Ocon, Fong, Bottas and Vergne head out.

Maldonado gets the weekend underway with a 1:48.739. Shortly after, Fong posts 53.867.

As Hamilton begins his first flying lap of the weekend, Bottas goes quickest with a 46.601.

Kobayashi is told that there is no telemetry and that the team therefore has no information on 'vital signs' such as tyre temperatures.

Hamilton posts 53.375, the Briton taking it easy, whilst teammate Rosberg heads straight to the top of the sheets with a 46.028.

No sooner has Bottas posted 45.913 than Hamilton bangs in a 45.141.

"Not the start we wanted for Will Stevens," admits Caterham, "he's had to jump out of car. We will find out what problem is and update you as soon as possible."

Button, Raikkonen and Magnussen, along with Stevens, remain the only drivers yet to post a time.

Game on! Rosberg goes quickest with a 44.860 as Hamilton goes purple in S2 but ultimately fails to improve.

Stevens' session appears to be over before it even began, Caterham confirming that it has "detected a technical problem".

Problems for Williams. As Massa reports a loose piece of bodywork, a very large chuck of the sidepod falls from teammate Bottas' car under braking for T11. Pat Symonds leaps into action with the crew.

All of which happens just before the end of the opening thirty minutes at which point the 'free' set of prime tyres have to be handed back.

Of course, the Williams duo is one of Rosberg's best hopes of thwarting Hamilton's title bid.

Ocon has incurred some damage at the front of the Lotus - right between the two 'nose prongs', thought to be due to 'bird strike'.

After thirty minutes, it's: Rosberg, Hamilton, Bottas, Alonso, Vettel, Massa, Perez, Kvyat, Vergne and Ricciardo. Stevens and Magnussen yet to post a time.

Vettel heads out, followed by Vergne and Ocon.

"Valtteri won't be back out in FP1 as the team need to repair the fixings on the chassis after bodywork came off," reveals Williams. "Team assessing Felipe's car."