An incredible atmosphere around the Tottenham Hotspur Stadium translated into early nerves on the pitch but it was the second most youthful squad in the entire competition who settled the quickest. Donny van de Beek gifted the freedom of White Hart lane to slot home a 15th minute opener.
A nasty head injury to Jan Vertonghen coincided with a tactical reshuffle that gave Spurs more balance and they ended the first half with a couple of efforts that threatened the Ajax goal.
An improved home side looked to push forward in the second 45 minutes but their lack of final third ability was evident in the absence of Harry Kane and Son Heung-Min.
Goalkeeper Andre Onana was barely troubled whilst a counter-attack down the other end resulted in David Neres striking the base of the post as Ajax recorded a crucial away win.
Busy van de Beek opens the scoring after tense opening
In a meeting nobody predicted during the early stages of the competition, the pre-match occasion was certainly befitting of a Champions League semi-final. A brand new stadium, described by many as the best on a planet, surrounded by a cacophony of noise as a vocal home support looked to match the hysteria created by the visiting fans on the streets of North London earlier in the afternoon.
22 years since Ajax last reached the final four, a period of time greater than the age of their captain, Matthijs de Ligt, the visitors were just two steps away from repeating their 1995 success. For Spurs, this was unknown territory. A first ever semi-final appearance with a quartet of former Ajax players in their starting eleven, including all three central defenders.
The opening ten minutes bred nerves and tension, neither side recording a pass accuracy above 75% as the ball was regularly given away in the final third by both teams. Van de Beek was the only man to get a shot away during that period, a wild lash over the bar.
Yet Ajax relaxed into the contest much earlier than their opponents as Spurs stepped off their Dutch counterparts. Dominating possession with 70% of the ball, the young pretenders soon made their passing prowess pay as the edge of the box rustiness disintegrated.
Dropping between the lines, Hakim Ziyech threaded a delightful ball to van de Beek who had been busy with his runs down the right channel. The 22-year old found himself with time and space between Danny Rose and Jan Vertonghen before comfortably slotting past Hugo Lloris for the opening goal of the tie.
Spurs recover despite Vertonghen blow
It was almost role reversal as the tension filtered to the stands and Ajax showed the confidence that had been vocalised around the ground before kick-off. A series of corners kept the pressure on Spurs before exquisite link up play between van de Beek and Dusan Tadic was only thwarted when the former was stopped by Lloris. A squared pass to David Neres would have provided a tap in for the Brazilian.
Spurs' main outlet was the strength and physicality of Fernando Llorente. The Spaniard, a key figure in the absence of Kane and Son, had a great opportunity to test Andre Onana but headed wide after peeling into space from a home free-kick.
The hosts were finally offered some respite but in sickening circumstances. Two Ajax graduates, Vertonghen and Toby Alderweireld, clattered into each other with the former coming off worse. In worrying scenes, Vertonghen hobbled down the tunnel appearing to be in substantial pain and shock. Moussa Sissoko was rushed back into first team action as Spurs reverted to four at the back.
Yet Alderweireld was almost the toast of North London moments later, heading a looping header onto the roof of the net from another home free-kick. With Spurs ending the half with all the momentum, Sissoko lashed a vicious effort wide with the last kick of the 45 minutes.
Structured Sissoko underpins Spurs improvement
Despite their positive ending to the first half, Spurs allowed Nicolás Tagliafico to stroll into space within a minute of the restart, the left-back skidding an effort wide from just outside the box.
Yet the game was starting to open up, feeding passion from the crowd. Dele Alli, on the periphery of the contest for the majority of the game thus far, volleyed a technical effort that bounced into the arms of Onana. He was then on the end of a Kieron Trippier cross, heading over after a pacy Spurs foray forward.
However, Ajax were able to hold firm during a lengthy period of conservation with Onana barely tested, ably organised by Daley Blind. And the energetic Dutch side possessed a danger of their own on the break...
Neres strikes the post
With little over ten minutes left on the clock, a burst forward resulted in the ball being worked to Neres, the South American attacker beating Lloris but striking the foot of the post.
At the other end, free-kicks continued to be the most promising outlet for the hosts, Alderweireld again heading over.
But for all of their huff and puff in the second half, Spurs will be extremely disappointed with the lack of clear cut chances they created in the home leg of this unlikely semi-final contest.
Yet we have seen them pick themselves up from the depths of Champions League despair before...
Takeaways from the game
Three at the back opened space for Ajax creativity
Mauricio Pochettino's decision to start with three at the back appeared to be a safe and secure defensive initiative on the face of the contest. Yet the lack of bodies in midfield allowed goalscorer van de Beek to pick off spaces between the lines. His growing influence on the game coincided with the shift in momentum after the first ten minutes in favour of the visiting side.
Danny Rose must add composure to his game
Rose is blessed with great pace and is a valuable asset to the Spurs squad. Yet in his determination to impress, particularly with added pressure to his place at club and international level, rash sliding challenges are creeping into his game. Here and in the last couple of Spurs matches, he has been walking a timing tightrope with challenges that are milliseconds away from conceding penalties.
This worry for Pochettino is perhaps why he did not start with four at the back in the first place.
Pace and strength has the ability to cause Ajax problems
The absence of Son through suspension was always going to be a big miss but on the odd occasion that Lucas Moura picked up the ball in space and drove forward, Ajax appeared fearful and dropped off the Brazilian. If Spurs can get their more pacy and powerful players into key areas during the second leg, then they have the ability to work this contest in their favour.
The introduction of Moussa Sissoko completely overhauled the Spurs performance, transforming the way they played through his sheer energy and physicality in midfield. Combined with the chances created from set-pieces, this young Ajax side appear potentially susceptible of wilting against stronger opponents.