Koeman headed into the Nations League quarter-final with Spain as a manager widely unpopular with Netherlands fans. While the Dutch had reached the EURO 2024 semi-finals, the only teams they beat in that tournament were Poland, Romania and Turkey, with Austria and an uninspired England side both claiming deserved wins over them.
By the start of the latest international break, he'd led his nation in nine matches against heavyweight opponents and hadn't won a single one, losing seven and drawing two. That record, along with a plethora of injuries - Nathan Ake, Stefan de Vrij, Denzel Dumfries, Ryan Gravenberch, Jerdy Schouten, Jurrien Timber and Micky van de Ven all missed out - left Oranje fans fearing the worst ahead of their two-legged tie with the European champions.
However, what followed were the two best performances of his second spell in charge as his side battled their way to 2-2 and 3-3 draws before falling on penalties.
A blessing in disguise
One major criticism of Koeman over the last few years has been that he's too set in his ways, both in terms of his player selections and his tactics, but he made big changes in both departments for the matches with Spain, although he was largely forced into them.
Prior to the matches, he'd predominantly played a 4-2-3-1 system that became a 3-2-4-1 in possession with right-back Denzel Dumfries bombing forward and right-winger Xavi Simons tucking inside to become a second number 10.
It worked at times, with Dumfries proving a powerful attacking weapon, but it left the team defensively vulnerable on the right-hand side, and the role Simons was given was one he struggled with.
What's more, the need to have a right-back that defended in a back four and a right-winger that sat narrow in possession left no room for Jeremie Frimpong, who has emerged as one of the Bundesliga's best players at Bayer Leverkusen.
Despite those issues, Koeman probably would have stuck with his usual setup if Dumfries was fit, but an injury to the Inter man forced the coach to come up with a new way to form his preferred shape - a box midfield - in possession. He opted to play Frimpong as an outright winger with RB Leipzig full-back Lutsharel Geertruida tucking into midfield behind him.
That wasn't the only long-awaited change, with injuries to others giving Bournemouth sensation Justin Kluivert and Brighton's Jan Paul van Hecke a chance to show what they could do.
When choosing them in his starting XI, Koeman may have felt that luck wasn't on his side with all those injuries to deal with, but a few days later, they're looking like blessings in disguise.
Van Hecke was a revelation alongside Virgil van Dijk at the back, both in and out of possession.
The 24-year-old gave away a penalty in the second leg but was rock-solid defensively aside from that moment and was incredibly composed on the ball, making a number of passes through the lines despite being pressed heavily by the Spanish forwards.
With Van Dijk preferring to play on the left, De Vrij and Matthijs de Ligt have been the two battling it out for the spot next to the Liverpool man since Koeman returned, but Van Hecke is much better physically than the former and much better on the ball than the latter.
If he continues to develop at Brighton and perhaps makes a move to a bigger club, the Netherlands could well have the stronger centre-back pairing in international football by the time the World Cup comes around.
The same can be said about their midfield three, with Kluivert forming a well-rounded trio with Frenkie de Jong and Tijani Reijnders.
The Bournemouth man did well with the ball in tight spaces, making a number of simple but effective passes that kept things ticking over, with one of them getting him an assist in the first leg.
His best work, though, arguably came off the ball. With the influence of Andoni Iraola clear, he pressed Spain tirelessly and constantly drew defenders away with runs in behind, making space for teammates.
Of those teammates, undoubtedly the most dangerous was Frimpong, who ran Marc Cucurella ragged in the first leg especially.
The 24-year-old hugged the touchline and looked to get in behind the Spanish defence every time he got the ball. With his blistering pace, most of the time, he succeeded.
He knew what to do with the ball after that too, making four key passes with lethal crosses and setting up his side's second goal in Rotterdam with one of them.
The missing piece of the puzzle
With this new system, the Netherlands will be able to field world-class players throughout the pitch once everyone is fit.
At the back, the ever-improving young goalkeeper Bart Verbruggen - who produced a stunning performance in the second leg - can have a formidable back four of Timber - ideally suited to inverting into midfield - Van Hecke, Van Dijk and Van de Ven or Ake in front of him.
In midfield, the trio of De Jong, Reijnders and Kluivert is only going to get better as the three get more used to playing together, and with them 27, 26 and 25 years of age, respectively, they still have plenty of room to grow individually.
On the wings, Frimpong and Cody Gakpo are two of the best wide players in football right now and have proven they're capable of scoring and creating goals against even the very best opponents.
Up front, though, things aren't as rosy.
Keen to move on from Memphis Depay and Wout Weghorst and find a new young striker to build around, Koeman gave chances to Joshua Zirkzee and Brian Brobbey at the end of 2024. However, while both had good moments, their struggles at club level have shown they're not exactly elite number nines.
Neither is Memphis, who was recalled in place of Zirkzee for the latest matches after impressing with his new club Corinthians in Brazil. He did score from the spot against Spain but struggled to make an impact for the majority of both games.
Emanuel Emegha seems next in line to be given a chance with the 22-year-old currently on 11 goals in 21 games for Ligue 1 side Strasbourg this season, but it's slim pickings beyond him. Thijs Dallinga is struggling at Bologna, while Leeds' Joel Piroe has been impressing in England's second tier but has never played at a top level.
Who then could be the striker the team needs? Well, if Koeman thinks outside the box, he could find that it's someone already in his squad.
The big victim of Oranje's new setup is Simons, who didn't start in either clash against Spain, with Frimpong starting on the right and Kluivert as the number 10. However, there could be space for him in the starting XI yet.
Koeman has largely stuck with Memphis in both of his spells as Netherlands manager because he wants a striker who can drop deep and link up play, who can hold up the ball and play in teammates running beyond him, and Simons is very much capable of doing that.
He's even done so as a striker before, occasionally playing as a 'false nine' for PSV in his first season in senior football and thriving there.
The 21-year-old showed in the second leg against Spain that he deserves to start, too. He came off the bench to set up Ian Maatsen's equaliser before equalising himself by converting a penalty he won after dancing past a defender and the goalkeeper in the box.
Van Hecke, Frimpong and Kluivert have shown Koeman that solutions can be found if he just tries new things, and this could be the biggest solution of all, one that could make the Netherlands capable of finally winning a World Cup.
