Two-time former winner Williams produced some sparkling snooker before the mid-session interval to reel in Hawkins from 5-3 and draw level at six frames each, and it seemed all the momentum was with the veteran Welshman.
But Hawkins returned from his dressing room rejuvenated and once more took a grip, moving 9-7 clear overnight in the best-of-33 clash of the two left-handers.
Hawkins, 39, has won more matches than any other player at the World Championship across the past five events and this year’s edition. Mark Selby has landed three titles in that time but Hawkins has reached semi-finals five times out of six.
Only once, in 2013, did he extend such a run to reach the final, and Ronnie O’Sullivan had his measure that time.
The Kent man began this tournament under the radar but there is nobody ignoring his claims on the title now.
O’Sullivan was back in Sheffield on Friday, six days after being knocked out in the second round by Ali Carter, but the five-time champion’s role was as a television pundit. His appearance in the arena before Hawkins and Williams arrived to resume their battle was a mere sideshow.
Williams failed to qualify for the World Championship last year and toyed with retirement, but picking up his cue again has proved lucrative, with the 43-year-old’s earnings already above £500,000 for the season.
With Hawkins twitching and frowning from his seat, Williams scythed into his opponent’s overnight lead.
A smooth opening 80 break set the early tone, and after they shared the next two frames Williams struck again. Both men were briefly distracted – Hawkins by an official’s walkie-talkie blurting out a message as he played and missed a red, and Williams by untimely encouragement from a spectator before he failed to sink a brown.
After giving Hawkins a playful nudge when their paths crossed, seemingly in a nod to the barge controversy involving O’Sullivan and Carter last Saturday, Williams produced a stunning pot on a crucial red.
In trouble by the baulk cushion, Williams had to apply heavy swerve on the white to sink a ball 12 feet away, and it effectively won him the frame.
The interval was no help to the Welshman though. The early fluency was gone, and when Hawkins doubled in the pink to make it three frames in a row it was a brutal blow.
Williams hit back with a precious 62 to ensure he would still be in the running on Saturday, when they play to a finish over morning and evening sessions.
In last night’s other semi-final, John Higgins maintained his two-frame advantage over Kyren Wilson after an intriguing evening session at the Crucible.
Higgins opened up a 12-9 lead, but Wilson responded with breaks of 106 and then 93 to get to within a frame of the Scot.
But Higgins rallied and a run of 91 saw him take a 13-11 lead into Saturday, where he needs only four frames to advance to the final.
Wilson trailed 9-7 going into the session and made an immediate statement with a break of 124 to halve the deficit. Breaks of 56 and 75, though, saw Higgins give himself a three-frame cushion before Wilson again rallied with a run of 81.
Higgins responded to again stretch his lead, but Wilson’s 50th century break of the season and then that 93 moved him within one again. Higgins kept his cool to win the final frame of the evening.