It cost the 26-year-old from Newcastle-under-Lyme a quarter-final against the game's biggest draw, Ronnie O'Sullivan.
"I can't be too hard on myself. I hope there'll be many more possibilities in the future," he told BBC Radio Stoke.
"It was good to go deep into a tournament and feel involved. I've not done that too many times."
The only other time Highfield had done so since turning professional in 2010 was at the Paul Hunter Classic in Germany in August.
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He also came through three matches there to make the last 16, but his progress at the York Barbican was a much bigger deal, as it came in one of snooker's "Triple Crown" of events.
Two 6-5 wins, followed by a 6-2 third-round success against Peter Lines, earned Highfield a best-ever pay cheque of £15,000.
Although he would have banked £22,500 for beating 1999 and 2003 world champion Williams, Highfield's efforts on his 26th birthday have given him a taste for more.
"The way I played against Lines, I can take a lot of confidence from that," he said.
"I've got used to playing small arenas, but it's about getting used to being out there in front of a massive crowd. Hopefully I can do that as much as I can."

John Askey's men were second-best on the day, but rallied in the last minute and striker Chris Holroyd bundled in from close range to draw his side level.
The Daggers nosed in front in the first quarter when Corey Whitely squared for Fejiri Okenabirhie, and the onrushing midfielder dispatched firmly into the bottom corner.
John Still's men remained in relative control before the interval, but could not put the match beyond doubt. Whitely struck the top of Craig Ross's bar on the stroke of half-time.
They remained largely on top in the second half, but were to be undone by Holroyd's sucker punch.
Report supplied by the Press Association.
Match ends, Dagenham and Redbridge 1, Macclesfield Town 1.
Second Half ends, Dagenham and Redbridge 1, Macclesfield Town 1.
Substitution, Dagenham and Redbridge. Shomari Barnwell replaces Jordan Maguire-Drew.
Goal!  Dagenham and Redbridge 1, Macclesfield Town 1. Chris Holroyd (Macclesfield Town).
Substitution, Macclesfield Town. Chris Sutherland replaces Danny Whitaker.
Substitution, Dagenham and Redbridge. Josh Staunton replaces Craig Robson.
Frankie Raymond (Dagenham and Redbridge) is shown the yellow card for a bad foul.
Corey Whitely (Dagenham and Redbridge) is shown the yellow card for a bad foul.
Second Half begins Dagenham and Redbridge 1, Macclesfield Town 0.
First Half ends, Dagenham and Redbridge 1, Macclesfield Town 0.
Substitution, Dagenham and Redbridge. Luke Howell replaces Fejiri Okenabirhie.
Paul Lewis (Macclesfield Town) is shown the yellow card for a bad foul.
Goal!  Dagenham and Redbridge 1, Macclesfield Town 0. Fejiri Okenabirhie (Dagenham and Redbridge).
First Half begins.
Lineups are announced and players are warming up.
Liam Highfield made for a frustrated figure at the UK Championship in York after his final-frame defeat by twice former world champion Mark Williams.
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Macclesfield earned a last-minute point from a 1-1 draw at second-placed Dagenham.