Ahead of today's opening session, the air temperature is 14 degrees C, whilst the track temperature is 16 degrees. Following an overnight storm the track is still dampish and there is the prospect of further rain to follow.

Tyre options this weekend are soft and supersoft, the latter, which features a new compound, making its 2015 debut. There is one DRS zone, and that's on the pit 'straight'.

This being Monaco, the risks being what they are, there are no third drivers or reserves on duty this morning.

While Lewis Hamilton will be keen to celebrate his new Mercedes deal with a win, teammate Nico Rosberg would love to take his third successive victory here, closing the title gap in the process.

This is a circuit where anything can happen - and usually does - in terms of the weather and the Principality's unique micro-climate and the ability to throw up shock results.

Due to the remaining damp patches, the session has been declared 'wet', though the sun, which has magically appeared, is doing its job and the storm residue is evaporating.

A late ERS issue is likely to limit Button's running this morning.

The lights go green and Ericsson leads Raikkonen and Bottas down the pitlane, all on Inters.

Most complete the sole installation lap, though Maldonado, Rosberg, Hamilton and Grosjean stay out for a second lap. Indeed, the Mercedes duo posts times, Hamilton crossing the line at 1:27.842 and Rosberg 33.180.

Despite being the only drivers on track, the pair are running remarkably close together.

Just six minutes in and everyone bar Button and the Manors have been out. The Yorkshire team making an emotional return here.

The two Manors emerge, whilst following a quick stop, Hamilton is also back on track, as is Rosberg, both now sporting the prime tyres. The Briton improves to 23.992.

More and more drivers return to the track, most following the Mercedes example and switching to primes. Ericsson goes third (36.150), only to be eclipsed by Ricciardo (26.987) and Verstappen (32.593).

Complaining of "abnormal rear locking", Sainz runs wide at Ste Devote.

Rosberg clouts the barrier at Tabac and heads into the pits, it's hard to tell if he incurred damage. Hamilton improves to 22.103.

As Vettel overtakes a Manor, Nasr gets it wrong at Ste Devote. Indeed, it's like Sunday afternoon for Vettel as he finds himself having to weave through the traffic.

Bottas is the latest to get it wrong at Ste Devote, a corner which has claimed so many over the years.

"I have no front warm-up whatsoever," complains Raikkonen. Nonetheless, he goes third, behind Hamilton and Ricciardo, with a 2..079 before improving to second with a 22.238.

Back to Ste Devote, where Ricciardo is thankful of the run-off, the Australian doing a quick reverse job and returning to the fray. Moments later it's Alonso's turn.

McLaren reveals that the crew is aiming to get Button on track "before 10am".

The 'free' half-hour comes to an end, Hamilton heads Raikkonen, Ricciardo, Vettel, Maldonado, Sainz, Perez, Grosjean, Verstappen and Hulkenberg.

While the rest return to the pits, Rosberg heads out on a brand new set of primes, thus enjoying a completely empty track, a rarity in Monaco.

Making full use of the free air, Rosberg improves to third with a 22.449, still 0.827s off his teammate's best. It's in the two final sectors where he's losing out.

That said, a 21.744 sees him close to within 0.122s of his teammate.

A 20.700 sees the German go quickest by almost a second, but Hamilton is back on track. Moments later the Briton posts 19.764. Rosberg responds with a 19.762. Game on!

Indeed, Hamilton bangs in a 19.196, over half-a-second quicker than Rosberg. Remember, this is where it all began to sour for the Mercedes pair last year.

Shortly after Stevens gets it wrong at Ste Devote, Ricciardo makes another short visit to the escape road.