A late goal from substitute Donyell Malen handed Netherlands a massive 4-2 win over Germany in their Group C 2020 Euro qualifier in Hamburg on Friday.
The Germans set out in search of their second win in a row against Netherlands following a last-gasp 3-2 win in the first group meeting between the teams in March and were in front inside of 10 minutes.
Netherlands had the better of the first-half possesion, but Germany looked more likely to score with Jasper Cillessen making a fine save on a Marco Reus shot just before half-time to keep the score 1-0 at the break.
"I told my players [at half-time] to stay in the game, not to give them so much space, control the ball better," Koeman told reporters. "That we should just keep going and we would get our chances. In the second half the Germans looked more tired and we benefited from that.
"Overall we worked harder than Germany for this victory."
The Dutch looked more threatening to start the second half and were soon level when Frenkie de Jong made a perfect first touch on a Ryan Babel cross and buried his shot past Manuel Neuer with his second to make it 1-1.
Minutes later Netherlands took the lead from a corner kick after Neuer saved a towering header from Virgil van Dijk with the rebound falling to Memphis Depay whose short cross from the near post was redirected into the goal by Germany defender Jonathan Tah.
A controversial De Jong handball gave Germany their chance to equalise from the spot and Toni Kroos sent Cillessen the wrong way with his penalty to even the score at two apiece.
Ten minutes before full-time, a Germany giveaway allowed Georginio Wijnaldum to sneak into the box and sneak a deft chip to Malen, who finished with aplomb past Neuer.
Wijnaldum put the result beyond doubt soon after, finishing off a swift counter-attack with a first-time finish from Memphis' whipped in cross to the travelling supports' delight.
"We played below our skill level and abilities," Germany manager Joachim Low told reporters. "The Dutch were the better team and we deserved to lose. We went ahead but I never had the feeling that we were in control of the game.
"The Dutch kept pressing and then we ended up playing high balls. That is not how we had planned to play. We will now need to analyse this game and draw our conclusions,"
The match was further proof of Germany's defensive issues as they conceded four goals in a match for the first time since a 2014 friendly vs Argentina. The last time it happened in a competitive match prior to the loss to Netherlands was in 2012 vs Sweden in a World Cup qualifier.
The result leaves Germany on nine points from four games, three behind leaders Northern Ireland, who they face on Monday in Belfast. The Dutch move up to six points from three games.