Mark Selby takes frame 15 and he's back within one of Ben Woollaston.

What price a deciding frame?

Their long potting could do with a touch of improvement, but the overall session statistics from John Higgins and Xiao Guodong confirm what a high quality eight frames we just enjoyed.

John Higgins will sleep easier after this frame.

He kills it in one visit with a break of 79 and that means it's 4-4 overnight.

He and Xiao Guodong return for another eight frames on Friday at 14:30 BST.

More of the same will do quite nicely.

Ben Woollaston holds his forehead as a chance to get to nine frames goes begging.

In fairness, to win the frame at that visit would have been extremely tough, with reds safe on the top cushion.

But there were enough available to build a good lead, and the red he misses is one he'd probably pot with his eyes shut if he wasn't closing in on beating one of snooker's legends at the World Championship.

"The pressure of the Crucible in a nutshell," says John Virgo on commentary.

Michael Emons
BBC Sport at the Crucible Theatre

Image source, Michael Emons

The trophies for snooker's three Triple Crown events - the World Championship, the Masters and the UK Championship - are all on display in the foyer just outside the arena.

John Higgins and Mark Selby have both won the World Championship on four occasions so will either man be able to get their hands on this piece of silverware again on Monday, 5 May?

Selby in particular has got work to do.

Michael Emons
BBC Sport at the Crucible Theatre

Image source, Michael Emons

The Crucible is a magical venue and looks just as special when you're outside with the famous sign lit up in different colours.

Where else would you rather be on a Thursday night?

Xiao Guodong is flying now and leads 4-3 against his 49-year-old opponent.

Xiao's composure on this big stage is impressing Stephen Hendry, who as a seven-time world champion knows a thing or two about handling these moments.

"He's turned into a real top player," said BBC pundit Hendry.

"He's won a tournament this year, he's got himself cemented into the top 16, and you can imagine him being there for a very long time.

"It's not as if the one victory in Wuhan was a flash in the pan. He's been at the business end of a lot of tournaments."

A very confident clearance from Ben Woollaston puts him two frames away from beating four-time world champion Mark Selby and setting up a second-round tie against Si Jiahui.

He's won four of the five frames played tonight and should have won the one he lost as well. It's not been the most free-flowing of matches in of heavy scoring and break-building, but he's been very impressive.

Ben Woollaston is at the table on a decent break with a four-point lead and three reds left.

Will he pull two frames clear?

Stephen Hendry
Seven-time world champion on BBC Two

Image source, PA Media

Another world-class pot. Brilliant from Xiao Guodong.

He was 3-1 down at the interval. Back on level . Every credit.

You won't see many better pots than you've seen there from Xiao Guodong to win the frame on the colours. Absolutely fabulous, and we're all square again.

Anon: Please could you explain the rules on replacing the colours on the table when their spot is covered? In what order does the ref look to other spots and at what point do they place it as near to the correct spot as possible?

If a colour can't go on its own spot after being potted, it is placed on the highest value colour's spot that is vacant - so the black, then pink, then blue and so on.

If all spots are covered, the colour goes as close to its own spot as it can - as you look at the table on TV, below the spot and in a direct vertical line with the spot.

Higgins opens a 42-0 lead but loses a grip of position and has to play safe.

The Wizard of Wishaw has annoyed himself there.

It's a mighty reprieve for Xiao who fights his way into a nine-point lead before being faced with a tough brown to the corner, knowing he'll probably leave it if he misses.

But he nails it, is ideal on the blue, and it's his frame. We're level here, and momentum is with the pre-match underdog.

Ben Woollaston is back in front and three frames away from one of the biggest wins of his career.

He gets himself into a position where Mark Selby needs two snookers to tie, but after the events of the previous frame, you can understand why he is taking absolutely no chances.

Some signs of frustration for Selby, who rolls the yellow ball down the table with a bit of ferocity after conceding.

It's interval time on Table One.

Image source, Getty Images

Katherine: Please could you explain the miss rule? And when does a free ball come into things?

There are nuances, but we will try to keep it simple...

A "miss" is called by the referee if a player has fouled and they feel the player has not got close enough to a ball they need to hit first to play a legal shot. It is called almost all of the time for foul shots in the modern era, and it is an attempt to stop players gaining any type of advantage by making a foul shot.

The "miss" gives the beneficiary three options; play the next shot from where the balls have landed, ask your opponent to play from where the balls are or ask for all of the balls to be replaced so your opponent can have another go.

If the result of a foul leaves a player snookered on the ball they are trying to hit next (or all reds still on the table), then a "free ball" is called. The player can nominate another ball on the table to effectively become that snookered ball and, if potted, it will be returned to the table.

What's the best way to respond to a barrage of heavy scoring?

Xiao Guodong shows us the way with a sublime 114 as the Wuhan Open winner serves up another reminder of his talent.

It has already been comfortably the best season of his career, and to topple John Higgins at the Crucible would perhaps top all his achievements.

Three more frames to play this evening. Let's hope they keep up this high standard.

Michael Emons
BBC Sport at the Crucible Theatre

Image source, Michael Emons

Those in the Crucible tonight may be in for a long evening. Mark Selby started 5-4 ahead of Ben Woollaston, who then took a 6-5 lead, with Selby edging the 12th frame on the black.

Play finished at 11:35pm last night in this match and it could be something similar tonight.

When the four players in tonight's session walked out earlier on, John Higgins was without doubt the most popular with plenty of 'Come on John' shouts from the fans.

His ers will be happy as he leads 3-1, although Xiao Guodong is on his way to pulling one back.

Image source, Michael Emons

Shaun Murphy
2005 world champion on BBC Four

I think whoever wins this frame now wins the match, such is the power of the potential mental damage the loss of that frame might have done to Ben Woollaston.

Ken Doherty
1997 world champion on BBC Four

Mark Selby has no right to win that frame at all.

Ben will be devastated. He has to sit there and contemplate that. He might have been better getting out of the arena and clearing his head a little bit.

A massive frame now, the last frame before the mid-session interval.

I have no idea how Mark Selby has won this frame!

The world number four needs a snooker with only pink and black left on the table, and the black tight on a cushion.

Somehow Ben Woollaston doesn't kill the frame off, the black springs free and Selby lays a snooker behind it, Woollaston misses it and then Selby knocks in an outstanding long pink into the corner.

The black falls too and Selby is back level.

Stunning.

Six of the 12 frames in this match have lasted longer than 30 minutes, including this one, with the average frame time close to 26 minutes.

I don't have the stats to hand but I would think that is the longest of any match in this year's first round.