Judd Trump bowed out of the UK Championship after losing the final five frames to Liang Wenbo, while Thailand's Thepchaiya Un-Nooh missed out on a ?44,000 windfall after failing to pot the final black when poised for a 147 break.
World number six Trump looked to be on course for a commanding win at York's Barbican Centre as breaks of 112 and 75 helped him open up a 3-0 lead, with Liang failing to pot a single ball.
The 2011 champion and last year's runner-up restored his three-frame advantage after his practice partner had pulled one back before Liang pulled off an astonishing comeback, with Trump making a series of uncharacteristic errors to hand the match to his opponent.
Trump said on Twitter afterwards: " Sorry for that performance. Feel like giving up after that!! Embarrassing!"
China's Liang said on www.worldsnooker.com: "In the last frame my head was gone and if it had gone 5-5 I think I would have lost. To beat Judd gives me a lot of confidence for the next match."
Tom Ford will be Liang's opponent in the last-16, after the Leicestershire potter's shock 6-1 win over Shanghai Masters champion Kyren Wilson.
Un-Nooh, meanwhile, missed the final black off its spot when set for a maximum 147 in what would have been a huge silver lining after a 6-2 defeat to 2013 champion Neil Robertson.
Un-Nooh bowed his head after seeing his final pot of the sixth frame rattle the jaws of the pocket. He lost the final two frames and lamented his missed opportunity.
Unaware that a maximum break would have earned him a big cash prize, the 30-year-old said: "I'm so disappointed. It's a nightmare. There was a lot of pressure on the black because I had never made a 147 in a tournament before."
Robertson sympathised with his opponent, adding: "I'm gutted for him. The money would have meant a lot to him, it would have covered his expenses for the next two years."
The Australian will next play Stephen Maguire, who earlier beat Mark Davis 6-4.
There was also a touch of late excitement in the match between Mark Joyce and Thailand's Dechawat Poomjaeng, who hit back from 5-0 down to triumph 6-5.
After winning the first five frames, Joyce then added just 66 points, 46 of them coming in frame 10, as Poomjaeng hit back in style.
Tuesday night's other contest saw Hong Kong's Marco Fu defeat David Gilbert 6-3 to set up a clash with Shaun Murphy for a place in the quarter-finals.
World number four Murphy coasted into the last 16 when he beat Ben Woollaston 6-2.
Murphy, champion in 2008, opened up with break of 83 and never relinquished control of the match.
The 33-year-old continued an impressive display of long potting as he went on to secure what was a comfortable victory with another impressive 106.
"I am very pleased with my performance," the 33-year-old said on the BBC.
"Part of going for your shots is saying, 'I am prepared to go for my shots, are you?'
"It sends a message out to your opponent. I have always gone for my shots and I always will."
Martin Gould defeated Mark Allen 6-4, which secured his place in the last-16 of the tournament for the first time.