Neil Robertson became the fifth former winner to lose in round one of this year's World Championship as Michael Holt earned a shock 10-6 success.
Both men scored two tons in a high-quality morning session, which ended with the qualifier leading 6-3.
Holt stayed in control, starting the evening with a 79 break and, after building a 9-4 lead, closed out victory despite some late jitters.
Mark Selby, another former champion, beat Robert Milkins 10-6.
But the 2014 winner had to show his trademark battling qualities to survive a determined comeback.
Robertson's shock exit means he joins 2015 champion Stuart Bingham and previous winners Shaun Murphy, Graeme Dott and Peter Ebdon in falling at the first hurdle.
Four-time champion John Higgins had no such concerns. The Scot rattled off three frames in a row to finish off a crushing 10-3 victory over Welshman Ryan Day and set up a last-16 meeting with Ricky Walden.
Hitman shows his strength
World number 28 Holt - nicknamed the Hitman - scored the highest break of the tournament so far, compiling a 140 during the opening session.
The 37-year-old, who has often talked about his mental struggles on the big stage, was pegged back to 3-3 but recovered with a nerveless 115 on his way to a 6-3 lead.
He stayed comfortably ahead in the evening session to set up a second-round meeting with close friend Mark Williams.
"I rode my luck at times, but I am really happy with my composure," Holt said.
"I have been here so many times saying I know I can play, but I just don't feel comfortable out there, so to go out there and feel comfortable was great."
Selby led 7-2 overnight but breaks of 50, 61 and 62 helped world number 21 Milkins move to within a frame.
But the Jester from Leicester's famed matchplay saw him win the next three frames to seal victory, despite not being at his fluent best.
Selby said: "Rob played some great snooker. But I knew he would let his arm go at 7-2 down. He put me under pressure.
"At 7-6, it got a little bit twitchy because it was not as if he got back playing scrappy snooker. He was scoring fluently and playing well.
"I have missed a couple of tournaments and felt a lot fresher, but I was not as match sharp. I didn't want to come into this tournament fatigued, so there were plusses and negatives."
Rounding up and looking ahead
Northern Ireland's Mark Allen won five frames in a row as he recovered from 2-1 down to go 6-3 ahead against debutant Mitchell Mann.
World number 11 Barry Hawkins leads China's Zhang Anda 6-3 after the first session of their match.
Both those games finish on Wednesday, while world number five Judd Trump begins his title quest against Liang Wenbo, and rising star Kyren Wilson takes on Joe Perry.
China's Ding Junhui, who had to qualify for this year's event, faces world number 12 Martin Gould in a match played to a conclusion in the evening.