A bright start from the Portuguese earned them two chances in the opening phase, showing the team's attacking intentions, whilst neither hit the back of the net.
Portugal were helped in their hunt for a spot in the semi-finals when AZ winger Ruben van Bommel, son of former Bayern Munich, Milan, and Barcelona midfielder Marco van Bommel, was handed two red cards in two minutes, the last of which for a late lunge on future Chelsea forward Geovany Quenda in the 21st minute.
The Netherlands' disastrous first 30 minutes continued when a tackle from Roma right-back Devyne Rensch earned Portugal a penalty after the VAR called referee Goga Kikacheishvili to the sideline. Quenda stepped up, but the Sporting Portugal talent hit the post and kept the score at 0-0.
The young Dutchmen hoped to have gone up 1-0 after 36 minutes, but a Portuguese own goal was ruled out for offside from Aston Villa's Ian Maatsen.
A massive chance followed soon as Stoke City's Million Manhoef beat Joao Muniz in a sprint and got the ball to striker Thom van Bergen, but the Groningen striker failed to convert on a possible golden opportunity.
After the break, the Netherlands couldn't emulate their pressure from the final minutes of the first half and mostly resorted to trying to make it through the game unscathed with ten men.
Despite the valiant defensive effort and little to no offensive production, Oranje broke free with speedster Ernest Poku, who found Bjorn Meijer in the box, but the left-back couldn't convert.
Poku continued to shine and became the Dutch hero in the 84th minute when the AZ winger opened the scoring. Maatsen played a perfect deep ball to Poku, who found the space behind the defence and calmly finished after evading Benfica stopper Samuel Soares.
After conceding their first goal of the tournament, it was all or nothing for Portugal, who brought on Wolves' Rodrigo Gomes for the final minutes. The defender, who scored twice in his last two games at the U21 Euros, couldn't force a breakthrough, however.
Portugal hadn't conceded a goal at the tournament, while the Netherlands mostly disappointed in Slovakia before finally winning their first game in their third group stage match. Still, it were the Dutch who pulled through and booked their second semi-final ticket in four years.