Jonny Clayton stunned Michael van Gerwen at the Grand Slam of Darts as James Wade continued his red-hot form to book a second-round place.
After an afternoon session in which Rob Cross became the first man to secure his place in the second round, the evening session saw Wade and Gary Anderson join the world champion in advancing early.
In-form Wade remains on course for a third TV title in as many weeks following a 5-3 success over Keegan Brown who will face Wesley Harms with the winner joining The Machine in the next phase.
However, the drama was in Group A, where Van Gerwen, chasing a fourth successive Grand Slam title and following his near flawless display on the opening night, looked like he was at it again until Clayton pipped him at the post in an astonishing penultimate match of the night.
Averaging more than 120, Van Gerwen won three of the opening five legs in 12, 11 and 10 darts but remarkably Clayton was keeping pace with a 112 average of his own to stay in the hunt and trail 3-2.
Van Gerwen added a 13-dart leg to move 4-2 in front but Clayton took out double eight to stay in touching distance before the defending champion managed to miss three darts for the match and The Ferret levelled before claiming the decider.
Van Gerwen's trebling deserted him and Clayton kept his cool for a 5-4 win that leaves him top of the group with four points.
In the same group, Gary Robson kept alive his own hopes of a place in the knockout stages with an equally remarkable 5-4 win over Joe Murnan, who somehow lost from 4-1 in front.
A spectacular burst from Robson, including three-dart combinations of 116 and 188, hauled himself back into the contest at 4-4 and even then there was time for Murnan to miss a couple of match darts before Robson pinned the winning double.
Gary Anderson produced the performance of the night in Group D as he blew Ian White away, hitting seven maximums in six legs. The Flying Scotsman averaged 112.54, and hit 5/7 doubles to leave 'The Diamond' with no answer. Anderson was at his very best as he secured safe passage through to the last 16.
Also in with a chance is Germany's Michael Unterbuchner, the BDO World Championship semi-finalist last year, produced a superb performance to send the Muffin Man Steve Hine packing.
An average of 97 and blistering finishing record of 71 per cent gave Unterbuchner a 5-2 win and set up his winner take all clash with Ian White.
In Group C, Wade stretched his winning streak to 12 matches, following up his titles at the European Championship and World Series Finals with another spectacular performance.
A 5-3 win over Brown featured a 104 average and three 100+ finishes to seal a place in the second round as he looks to go one better than his runner-up finishes in Wolverhampton in 2010 and 2016.
Mark Webster's hopes of qualifying are over after a 5-3 defeat to Harms who will now face Brown on Tuesday night.
The Dutchman stayed alive with a dogged display against Webby who took the first leg but couldn't get going as Harms took control with a run of four successive legs and closed out a win that keeps him in contention.
Michael Smith prevailed in the clash of Saturday's winners in Group B finding a brilliant 13-dart leg to beat Krzysztof Ratajski, who would have gone through with a victory, in a final leg decider.
Smith rallied from Ratajski's burst that took him into a 3-1 lead but as his scoring deserted him, Smith, one of the heaviest scorers in the game, was able to take advantage.
The Premier League runner-up's patience was rewarded with a run of three straight legs to move within one of the match - surviving a scare as Ratajski missed a dart for a 110 finish and a 4-3 lead himself.
The Polish Eagle did manage to force the decider before Smith triumphed to ensure the group remains in the balance following Raymond van Barneveld's win over Adam Smith-Neale which showcased all the ups and downs of his season so far.
Barney, the 2012 Grand Slam champion, had chances to be well clear before eventually edging out his BDO opponent in another final leg decider that saw both men miss match darts as nerves took hold.
Barney took the first, third and fifth legs and missed darts in the second, fourth and sixth to allow Smith-Neale to remain alive in the tournament.
Van Barneveld then cleaned up 76 in two darts to move within a leg of the match but Smith-Neale took out a timely 110 finish before the dramatic finale that saw Barney pin double 10 for the crucial two points.
Groups A-D will reach their conclusion on Monday night with Groups E-H finishing on Tuesday before the knockout stages get underway with Wednesday and Thursday's second round when the matches are the first to 10 legs.
The Grand Slam of Darts continues on Sky Sports across the week with the group stages reaching their conclusion on Monday and Tuesday, Monday's evening session is underway on Sky Sports Action from 7pm
Keep up to date with the news as the tungsten enters its busiest time of year with the PDC World Championships just around the corner get all the latest at sky.mnosports.com/darts and join in the conversation @SkySportsDarts.