World Champion John Higgins paid the price for a missed pink in the sixth frame as he was dumped out of the 888 Welsh Open by Ding Junhui in the second round.
Higgins appeared poised for a 4-2 victory but he missed a pink off the rest and allowed Ding to tie it a 3-3 before a break of 86 sealed the win.
All the drama of the match was in the sixth frame, which saw Ding make a break of 61 to seemingly take control.
But a missed black gave Higgins a sniff and he made a break of 58 before the pink cost him and Ding forced a decisive seventh.
Higgins missed a long red early on and Ding made him pay with a decisive break to set up a meeting with either Stephen Lee or Tom Ford in the last eight.
The other second-round match played on Wednesday evening proved far more straightforward as Shaun Murphy brushed aside an off-colour Steve Davis 4-0.
Murphy will now face Stephen Hendry or Mark Allen in the next round.
The afternoon session saw the first round completed with Ronnie O'Sullivan appearing in fine form as he brushed aside Marco Fu 4-1.
O'Sullivan's performance at the Newport centre ended any fears over his top-16 place ahead of April's World Championship, ensuring he will qualify automatically for the Crucible.
Coming into the game off a victory in Berlin 10 days ago, he was quickly into his stride with a break of 52, and an 88 put him two frames to the good.
He made 51 in the third but a missed black off its spot allowed Fu to pinch the frame.
But it was only a blip for the former world number one, who wrapped up a 4-1 win with a superb 102 break.
"The event in Germany is history and this is what's important now," said O'Sullivan on worldsnooker.com.
"I was a bit nervous today because after winning the last tournament I didn't want to go out in the first round. So it was good to get my hand on the table and pot some balls early on.
"Marco missed the blue when it looked like going 2-2 so it could have been different. He's got a good record against me and feels comfortable against the top players so it was a tough draw."
Allen did not have to be at his best as he hammered Ken Doherty 4-0.
Doherty missed an opportunity to take frame one and another miss was punished as Allen went 2-0 up.
The Northern Irishman was not winning frames at one visit, but made half-centuries in the two remaining frames as he inflicted a whitewash on his out-of-sorts opponent from across the border.
Home favourite Matthew Stevens set a new tournament high break as his high-quality win over Barry Hawkins went the distance.
Stevens came from 53-0 down to win the opener, fluking the decisive pink, before Hawkins got over the line on the colours in frame two.
Stevens won the next in one visit with a sparkling 141 but Hawkins raised his game in response, breaks of 71 and 123 taking him 3-2 ahead.
A 70 break helped Stevens take the match to a decider in which he made 60 before an unlucky positional shot and, after Hawkins jawed a long red and went in off, knocked in the decisive red.
That earned a clash with Stephen Maguire, who saw off Wiltshire qualifier Adam Wicheard 4-2.
Maguire made 54 in the first and moved into a commanding 3-0 lead after back-to-back centuries, 101 and 131.
Wicheard, who beat Liu Song and Marcus Campbell to qualify for the tournament, finally got on the board and cut the deficit to 3-2 with a 54 but Maguire sealed victory with an 87 in frame six.