Piers Newbery
BBC Sport at the O2 Arena in London

Image source, Getty Images

"After 24 hours of poor maths, double-checking and questions that begin with "so does it come down to sets won or games percentage….?", it's all very simple. And I am yet to find anyone who thinks Murray will beat Federer in straight sets. That makes sense based on recent history but probably underplays the fact that they have an 11-11 head-to-head record, and there is something on the line for Federer tonight as a defeat would probably leave him facing Djokovic in the semi-finals. An unenviable task at the moment."

Andy Murray last beat the Swiss superstar in straight sets in the Shanghai Masters semi-final in October 2012 - 6-4 6-4.

For those of you, like me, who might have been preparing to scour the archives for the last time the ever popular Roger Federer lost in straight sets - to anyone - fear not.

It happened as recently as the Paris Masters quarter-final when Milos Raonic won 7-6 (7-5) 7-5. This is what it looks like.

Image source, Getty Images

BBC Radio 5 live sports extra pundits have been having their say on the Federer-Murray rivalry.

Colin Fleming, Andy Murray's Great Britain Davis Cup doubles partner, says: "We hear them both say it is a pleasure to play each other, but they get under each other's skin on court and really want to beat each other. I'm expecting a real fierce encounter."

Miles Maclagan, Andy Murray's former coach, says: "I think a lot of that came from the time before Murray had won his Grand Slams and in the media we talked about 'the big four'. Federer probably felt 'why are you putting him in our class?' Until recently, Andy had a winning head-to-head record against Federer, which he wouldn't have liked."

Commentator David Law offers: "There was that moment when Andy Murray got to the final of the 2010 Australian Open and Federer made a comment along the lines of 'It's a big day for Andy, they haven't won a Grand Slam in about 150,000 years'. And there have been a few other barbs along the way."

Image source, Getty Images

While Murray and Federer themselves talk of "great respect" and offer little hint of any animosity, those in and around the dressing rooms on tour suggest there's a fair bit of niggle between the two.

We'll be watching carefully for body shots, trash talk and a lack of tennis etiquette if this one turns ugly.

Murray's chances have not been helped by Kei Nishikori's three-set victory over David Ferrer earlier today. The Spaniard was a late replacement for Canada's Milos Raonic, who pulled out at lunchtime with a quad injury. Here's how Group B is panning out following that result.

There's nothing like an important Andy Murray tennis match to divide public opinion.

We'll be running a vote until just before tonight's encounter begins and we want you to have your say on whether Murray will beat the 17-time Grand Slam champion.

Just head to the right of the screen and cast your vote - or tweet to @BBCSport, external 'yes' or 'no'.

What a rivalry this has been over the years. In 22 meetings, they are tied at 11 wins apiece. Murray leads 6-2 in their Masters matches but Federer has a 4-1 lead in Slams and has won both their meetings this year. The Swiss has also won all three of their previous meetings at the O2, where both players are expected to receive huge support.

I say within reach. In truth, it's a tall order facing Murray against the 17-time Grand Slam champion, who is already through to the last four. In order to join the Swiss in the semi-finals, Murray must not only win, but win in straight sets.

Image source, Reuters

It's been a tough old year for Andy Murray. Struggling to overcome the effects of back surgery, losing his Wimbledon crown, dropping outside the world's top 10 for the first time since 2008 and getting himself into a political pickle over Scottish independence.

And yet, following a recent upturn in form, there is still hope of a glorious ending to 2014 for the British number one.

Tonight he takes on his great rival Roger Federer at the O2 Arena in London with a place in the semi-finals of the World Tour Finals still within his reach.