John Higgins of Scotland reacts in the quarter-final match against Neil Robertson of Australia on day eleven of the 2019 Betfred World Snooker Championship at Crucible Theatre on April 30, 2019 in Sheffield, England.
Gilbert produced 56 to move 11-6 ahead from the morning session with Higgins promptly winning the 18th frame with a stunning black up and down the table to close to 11-7 behind.
The next two frames were shared, Gilbert running in 75 in the 19th frame, as the match headed to the mid-session interval with Gilbert 12-8 ahead.
Higgins brilliant black boosts hopes
A 143 from Higgins was cancelled out by a 91 from Gilbert, but the four-times world champion steeled himself superbly to win the final two frames of the session to close to 13-11 behind.
They play to a finish from 2:30pm on Saturday with the first man to 17 frames reaching the final.
A stunning blue by John Higgins
SECOND SESSION REPORT
David Gilbert has extended his advantage over a struggling John Higgins to 10-6 after claiming the final frame of Friday morning's World Championship semi-final with a nerveless pot on the black.
Four-times world champion Higgins - who is chasing a third successive final appearance at the Crucible - resumed 5-3 behind and looked badly out of touch in the morning session in Sheffield as he made numerous safety errors in losing the first three frames of the day to fall 8-3 behind.
Tamworth potter Gilbert - who has reached finals at the World Open and German Masters this season - had opened the session with an immaculate clearance of 125, a break that set the tone for the early part of the exchanges.
Gilbert starts off with a century
Scotsman Higgins missed a green in the 12th frame that looked likely to cost him another frame, but was fortunate not leave it before being handed a reprieve as he mopped up the remaining colours to win his first frame of the day in trailing 8-4.
Despite managing to claim the next two frames after the mid-session interval with breaks of 67, 52 and 58, Higgins was never convincing as 16th seed Gilbert picked up the 15th frame to ensure he would protect a lead going into the third session of the match on Friday night.
Both men had chances in the 16th frame, but Higgins could not launch a counter attack as he broke down on 50 with Gilbert returning to the table to open up a four-frame advantage before they play their third session on Friday night from 7pm.
Gilbert pots blue direct from break-off
The first player to 17 frames earns a place in the final against Judd Trump or qualifier Gary Wilson, who are locked at 4-4 after their opening session.
Qualifier Gary Wilson produced an immaculate 140 break as he came out of the first session with Judd Trump level at 4-4 in their World Championship semi-final at the Crucible Theatre.
World number 32 Wilson had several chances, and may count himself unfortunate not to have an overnight lead from his joust with the Masters champion.
Wilson opened with a break of 61, but lost the first frame before edging a scrappy second frame and then piecing together a brilliant 140, the second highest break of the tournament behind Trump's 141 in the first round.
Trump made 54 to restore parity at 2-2 before he dominated the fifth frame for a 3-2 advantage.
Wilson was not perturbed as he established himself in the next two frames for a 4-3 lead. The Tyneside player had chances to open up a 5-3 overnight, but Trump finished matters off with a 54 after Wilson failed to slot the penultimate red with a spider down a side cushion.
They begin their second session at 2:30pm on Friday afternoon.
In the other semi-final, 16th seed David Gilbert continued his fine form to take an early 5-3 lead over four-times world champion John Higgins in Sheffield.
Higgins had beaten Neil Robertson 13-10 in an epic to reach the last four, but failed to click in an opening session that saw Gilbert play the better snooker.
A century break of 113 was the highlight for the Englishman, who won five of the six frames before the break to take an early lead with plenty of action still to come.