Jamie Jones held his nerve to cause the second major upset of the World Championship by ousting 2005 champion Shaun Murphy in the first round.
The Welshman was poised for victory at 9-7 ahead when he missed a straight red, allowing Murphy to make it 9-8.
Despite missing another red when poised to take the next, the 24-year-old Crucible debutant then knocked in a smooth long red to get over the line.
Compatriot Matthew Stevens beat Marco Fu of Hong Kong 10-3.
Stevens, a finalist in 2000 and 2005, built an 8-1 advantage in the morning session and swiftly completed a comfortable win.
Murphy, the world number five, is the second contender to fall in the opening round after Mark Allen's exit on Sunday.
Jones, ranked 36 in the world, won four frames in a row from 7-5 down to rock the two-time finalist and will face either Stephen Lee or Andrew Higginson in the second round on Sunday 29 and Monday 30 April.
The 24-year-old from near Neath had shown his potential by thrashing world number 15 Ricky Walden 10-2 in the final qualifying round, and also beat reigning Crucible champion John Higgins at the PTC Finals in Galway last month.
"I've never felt any pressure like it in my life," said Jones after the biggest win of his career to date. "I've never known an occasion like it.
"For my Crucible debut I think I played pretty well. That's definitely not my best though. I can play better than that.
"Everyone in the village where I live has been watching on TV and my phone hasn't stopped going since I left the table. It'll be like a circus at home."
Murphy, five times a Crucible quarter-finalist, said: "It's certainly not how I saw the tournament going. I thought the match was really high quality.
"I really enjoyed it, which sounds funny considering I got beaten. I thought Jamie held himself together really well and he didn't play like a debutant. I've certainly played a lot worse myself and won before."