Winstanley, who joined the PDC circuit in January and was a semi-finalist in the Grand Slam of Darts last month, continued his emergence with an impressive first win on the Alexandra Palace stage.
The former Lakeside Championship finalist hit ten 180s and came from 2-1 down in sets to firstly force a decider before taking a 6-4 victory in a tie-break to end a see-saw fifth set.
"I never make it easy for myself but I^m one of those battlers who won^t give in," said Winstanley, who now plays either Vincent van der Voort or Stuart Kellett in the second round.
"Both myself and Mervyn wanted to go up there and give the fans a good exhibition, but it always seems to be me going the distance in matches and I^m just glad I came out top.
"It means everything for me to get through that and it^s a big thing for me. It was a battle and it was very good entertainment, and we^ll see what happens now in the second round."
King, October^s World Grand Prix runner-up, had one dart himself to take victory, but admitted: "Dean played much better than me in the overall scheme of things.
"For the last week leading up to this, I^ve been on fire in practice and I didn^t find the happy medium on stage today."
Former Lakeside Champion Steve Beaton was also pushed early on in his first round win over Australia^s Kyle Anderson, the Oceanic Masters winner who took both of the first two sets to a deciding leg before the Englishman prevailed to set up a clash with number three seed James Wade.
"I^m glad to get through and I can settle down and get on with things in the second round," said Beaton.
"All my plans went out of the window when I got on stage tonight, and to be fair to Kyle he could have been 2-0 up too but he missed chances and I made the most of it."
Dennis Priestley, the PDC^s first World Champion in 1994 who has qualified at the age of 62, will play Ronnie Baxter on his return to the Alexandra Palace stage, while former world number one Colin Lloyd meets Darin Young and Justin Pipe faces Andy Jenkins.