That's probably about as close as Sheffield United have come in this second half, though Steven Davies's snap shot from the edge of the area doesn't trouble Wes Foderingham.

Meanwhile, John Swift replaces Ben Gladwin, who missed a penalty for Swindon before the break.

Daniel Jones will have had his heart in his mouth there. The Spireites defender plays a back pass that is well short, but Tommy Lee just about beats Jermaine Beckford to the ball and clears.

Speaking of Sam Ricketts, he's just become the first Swindon Town player to go into the book for a foul on Ryan Flynn. That looked a relatively straightforward one for the referee.

Image source, Getty Images

I'd say these next 10 or 15 minutes could be absolutely crucial to the overall complexion of this tie, as Swindon Town now have a real foothold.

There's been an awful lot of groaning around Bramall Lane since Sam Ricketts headed the Robins' equaliser five minutes into the second half.

Image source, PA

Remember Preston have only won three times in 21 play-off appearances. With just under half an hour to go here, they are on the back foot but the home side still cannot find a way through.

Aston Smith: Preston players going down a little too easily tonight. Man up! We complained when Man Utd did the same thing.

John Threlfall: Preston and play-offs have been a bad combination in the past, praying this time it's different!

Use #bbcfootball on Twitter to get in touch.

The two Swindon Town wing-backs, having been pegged back before the interval, are now finding a good deal of space down either flank.

This time Sam Ricketts gets forward down the left, but as he tries to shape a right-footed curler into the far corner it's blocked away.

Replays have suggested Spireites midfielder Jimmy Ryan is a very lucky boy to still be on the pitch. It appears he struck Paul Gallagher with an elbow, but the referee may not have seen it from where he was standing.

He ended up booking both players.

The Blades are struggling to get up the pitch here, and when they at long last do get inside the Swindon half Kieron Freeman has a rush of blood to the head and blazes a shot wide of the near post from long range.

Almost a piece of magic from Chesterfield's Gary Roberts. The winger weaves his way into the area but slices his shot just past the left hand post.

The hosts are pushing for an equaliser here.

Sheffield United have won 13 out of their 16 meetings with Swindon Town at Bramall Lane, but that Sam Ricketts goal has the Robins supporters in full voice behind Mark Howard's goal.

For the record, there are 20,890 people inside the ground tonight.

Ian Woodcock
BBC Sport at Bramall Lane

"It's been a good start to this second half from the visitors and that goal has really given them something to hang on to. Sheffield United simply haven't got going yet and boss Nigel Clough is cutting an agitated figure on the sidelines."

Image source, Getty Images

Things are in danger of getting out of hand here. Chesterfield's Ian Evatt slides in late on Joe Garner, but for once there are no afters.

Referee Mark Haywood is going to have a job to keep things in control. Plenty of niggle out there.

Image source, Getty Images

A superb, superb set-piece goal from Swindon Town.

Nathan Byrne's outswinging corner is met by the head of Sam Ricketts, and the big defender on loan from Wolves guides a fantastic header across goal and into the corner of the net.

Swindon have started this second half exactly as Sheffield United started the first - on top. However, for all their possession play they've not quite shown a cutting edge just yet.

Less than two minutes into the second half and there is another confrontation between both sets of players. It was sparked after Chesterfield's Jimmy Ryan appeared to throw an arm at Paul Gallagher.

Both players are booked, but that could have easily been red for Ryan.

Ross Whitehead: Chesterfield been by far the better team in that half. We just need to create a few more chances and take them.

Keep your thoughts on tonight's play-off games coming in using #bbcfootball on Twitter.

The first chance of the second period goes the way of the visitors, but Michael Smith can't direct his header on target. The big man was at full stretch, so he's certainly not to blame.

And we're under way in both of our play-off semi-final first legs once again.

We've got a half-time substitution at Bramall Lane, which sees Stefan Scougall replace John Brayford for Sheffield United.