Following the 1-1 draw between Feyenoord and Ajax earlier on Sunday, PSV were no longer set to win the Eredivisie title in round 28, with their lead growing to 18 points at most with a win away at Telstar, who spectacularly beat PSV in Eindhoven earlier this season.
Peter Bosz started the game with Ricardo Pepi as his striker, just one day after the American international saw a 36-million-euro move to Fulham collapse.
After another superb solo from Ismael Saibari, Ricardo Pepi looked to have opened the scoring after sliding the ball under Ronald Koeman, but the American saw Danny Bakker spectacularly clear the ball off the line to keep the game scoreless.
PSV were reduced to ten men when Roma loanee Anass Salah-Eddine was given a straight red card for dealing Gerald Alders an elbow to the chin, leaving PSV to play the last 50 minutes with a handicap.
It all went from bad to worse for the champions-to-be after Sem van Duijn headed a free-kick to the far post, where Patrick Brouwer was eagerly waiting to fire the ball past Kovar and give Telstar the lead shortly before half-time.
It took PSV just 80 seconds to level the scoring after half-time, thanks to Kilian Sildillia, who nodded in a corner from Ivan Perisic and earned the star winger his ninth assist of the season.
PSV took control of the match and tested Telstar following Sildillia's goal, but were left with one goal as none of Ryan Flamingo, Couhaib Driouech, and Ismael Saibari could give the visitors their first lead of the afternoon.
Telstar kept up the fight and rewarded themelves for a strong outing against the reigning champions when Sem van Duijn beat Kovar from distance to give the hosts a shock lead in the 66th minute.
The BUKO Stadion exploded once more when Kay Tejan, who was brought on just seconds before, doubled Telstar's lead after Sem van Duijn's long throw-in fell favourably for the striker, who calmly put it past Kovar in the 74th minute.
Following Brouwer and Van Duijn's goals, Tejan became the third former player of amateur club Quick Boys to score against PSV. All three played at the amateur level in the past five years, with Brouwer even being the reigning Quick Boys Player of the Year.
The chances kept piling up for Telstar, who came close to a stunning fourth when Devin Koswal had a rocket saved by Kovar at his near post.
PSV pushed in the final minutes and thought it had scored a late consolation goal, but Ismael Saibari's backheel goal was quickly ruled out for offside, meaning Telstar had completed a truly miraculous double over PSV with the second win over the reigning champions in their first Eredivisie season since 1978.
What could've been a championship decider turned out to be a disaster for PSV, who lost to a promoted team for the second time in one season for the first time since 1958. PSV's next opportunity to win the league will be on Saturday, April 4th, when they host FC Utrecht in Eindhoven.