Brent Pilnick
BBC Sport at Sandy Park

Saracens are champions for a reason. They've hardly had any of the ball in the opening 10 minutes, but when they have had it they've looked slick and effective in attack.

Exeter look a bit nervy early on, but the deafening crowd here at Sandy Park will give them heart.

They may be trailing in the early stages here, but Exeter have come into this semi-final absolutely flying.....

Image source, Getty Images

Another mental victory for Exeter as they force a penalty against Saracens at the scrum and Mako Vunipola is the guilty party there.

Huge cheers from the home fans for that.

Saracens up the pressure again as Chris Ashton pushes Phil Dollman out of touch inside his own 22.

Great kick-chase from the visitors to hunt that down, but surprisingly Jamie George's first line-out is intercepted and Exeter escape further damage on the scoreboard there.

Straight through the middle for the England and British and Irish Lions man.

Saracens are off and running and now the home fans are hushed for the first time this afternoon.

Image source, Getty Images

Early penalty for Saracens and Owen Farrell as Exeter are penalised for going off their feet at the breakdown on their own 10-metre line.

First chance for the visitors to get on the board....

Brent Pilnick
BBC Sport at Sandy Park

What an afternoon for young Exeter scrum-half Stuart Townsend.

On New Year's Eve, he was playing on loan for the Cornish Pirates against Nottingham in Penzance in the Championship, but five months later he starts the biggest game of the season against the double European champions.

Exeter do have experience on the bench in the form of Will Chudley, but the 21-year-old will have to be at his best against the likes of Farrell, Ashton, Itoje and the Vunipola brothers his afternoon.

Exeter come out firing and looking to test Saracens' back line under some high balls from Stuart Townsend.

Alex Goode has the answer one up and under, allowing the European Champions to settle some nerves.

And we're off!

Wayne Barnes is the man in charge of this one and Owen Farrell gets us going with his boot for Saracens!

Here come the two teams.

Saracens step out first in their bright red shirts, Exeter follow them in their black strip.

The noise is electric around Sandy Park....

Image source, Getty Images

Hmm, looks like we could be on for a bit of a mudfest in both games...

Exeter forecast:

Coventry forecast:

....and just before the teams step out at Sandy Park, the skies look apocalyptic!

Think they're in for a bit of a soaking soon.

Image source, Rex Features

There's already been some semi-final drama in the city of Exeter this week.

On Thursday night - the football club booked their place in a London final next weekend when Jack Stacey's 95th-minute strike secured a win against Carlisle United and a spot in the League Two play-off final at Wembley next Sunday.

Could the Chiefs make it a big Devon double final weekend with victory over Saracens this afternoon?

Image source, Rex Features

There was absolutely nothing to separate these two sides when they last met in January at Allianz Park.

Fourteen-man Saracens battled back to an impressive 13-13 draw against Exeter, which put them top of the Premiership at the time.

The game turned after 10 minutes when Sarries prop Richard Barrington was sent off for a high tackle.

Gareth Steenson converted the resulting penalty and Jack Nowell's try gave Chiefs a 10-3 lead at half-time.

But, Saracens performed admirably after the break and rescued two points when Titi Lamositele was forced over the line and Alex Lozowski converted.

I think they might have.

Almost a year ago, these were the scenes at full-time of the 2016 Premiership final.

The agony.....

Image source, Getty Images

.....and the ecstasy.

Image source, Getty Images

Saracens were 28-20 victors at Twickenham last May and withstood a late rally by the Chiefs to secure a European and domestic double.

Can Mark McCall's men back that up after being crowned Champions of Europe again last Saturday or will the Chiefs ruin the script?

Image source, BBC Sport

So this is where the top four in the regular season go head-to-head for the chance to be a step closer to claiming the Premiership trophy.

Wasps finished top of the table with a 35-15 win against Saracens on the final weekend and just pipped Exeter to the summit on the back of more games won.

The Chiefs warmed up for this weekend with a 34-20 win at Gloucester while Leicester prepared for their 13th successive play-off appearance with a 28-23 victory at Worcester.

A real treat for rugby union fans on the way this afternoon as the domestic season moves towards its finale.

Who do you think will come out on top in these semi-finals? Which players will prove the match-winners this afternoon?

Tweet using #bbcrugby and let us know your thoughts.

Image source, Getty Images

Exeter head coach Rob Baxter told BBC Spotlight:

"Feeling that you can win anywhere is very important and Saracens have that but I'd like to think we've got an element of that as well because of our run in the Premiership recently when we've won home or away and seen off all comers.

"Having said that, we haven't seen off Saracens this season, so it's going to be a great challenge for us.

"We've talked for a long time this season about what it would take to become champions, and one of the things you've got to be prepared to do is either beat the team that beat Saracens or beat Saracens yourself."

Brent Pilnick
BBC Sport at Sandy Park

Image source, Rex Features

Exeter fans will hope recent history doesn't repeat itself this afternoon against the reigning champions.

The Chiefs have failed to beat Sarries in any of their past five meetings - including last year's Premiership final and a draw at Allianz Park earlier this season when Mark McCall's side were down to 14 men for much of the game.

You have to go back over two years to the last time Exeter had a win over their opponents - a 24-20 away win in the penultimate game of the 2014-15 season.

We've got every kick, ruck and maul of this first semi-final covered on BBC radio for you this afternoon.

BBC Radio 5 live Sports Extra are in position at Sandy Park with presenter Sara Orchard joined by Jerry Guscott and Ian Robertson on commentary, which is available online, via Freeview television and DAB digital radio.

Watch Jerry and Sara's video preview by clicking or tapping the link on the tweet below....

You can also tune into both BBC Radio Devon or BBC Radio London to hear every second of the action.

Make your listening choice by selecting the live coverage options at the top of the page

Exeter head coach Rob Baxter is blessed with the return from injury of several key men for this semi-final.

Don Armand and Thomas Waldrom both feature in the back row while Phil Dollman is recalled at full-back.

Gareth Steenson skippers from fly-half, James Short lines-up against his former club on the wing, while at centre Steenson’s compatriot, Ian Whitten, will run out for his 100th league appearance for the Chiefs.

England centre Henry Slade is among the replacements.

Image source, BBC Sport

Replacements: Yeandle, Rimmer, Francis, Lees, S Simmonds, Chudley, Slade, Campagnaro.