London - Tottenham manager Mauricio Pochettino admitted he was at fault as Ajax closed in on a first Champions League final for 23 years thanks to Donny van de Beek's early goal to win the first leg of their semi-final 1-0 on Tuesday.
Van de Beek's opener on 15 minutes was just reward for the Dutch side's first-half dominance as Tottenham badly missed the presence of the injured Harry Kane and suspended Son Heung-min.
Tottenham improved after the break despite another injury blow as Jan Vertonghen had to be helped down the tunnel after a sickening head knock, but lacked the inspiration needed to get back on level terms without their two top scorers.
"Watching now of course I can accept it was a mistake the shape we used. But there were not too many options," said Pochettino.
"I am not happy, but our lack of energy from the beginning made our game difficult. We were a little sloppy."
Ajax had shown they are not fazed on the road despite the tender age of many of their squad by shocking Real Madrid and Juventus away to reach the last four and started confidently.
Hakim Ziyech's through ball picked out midfielder Van de Beek who took his time to leave Hugo Lloris prone before slotting into the bottom corner.
"I think it was an amazing evening, an amazing result," said Ajax coach Erik ten Hag.
"In the beginning we very strong, we were completely dominating the game and we made a fantastic goal."
Lloris kept his side in the game 10 minutes later from another Van de Beek effort as Ajax threatened to run riot.
"The way we conceded the goal was so painful, I think we were so poor in this action," added Pochettino.
"They showed more energy than us, but I think after 30 minutes we started to equalise the game."
Spurs miss Kane and Son
On top of Kane and Son, Spurs were shorn of the injured Erik Lamela and Harry Winks and lost another key player when Vertonghen came off worst as he contested a high ball with Ajax goalkeeper Andre Onana and team-mate Toby Alderweireld.
The Belgian was patched up and briefly returned to the field before having to be helped down the tunnel leading to questions over why the Spurs medical staff allowed him to continue.
"I wasn't involved," insisted Pochettino. "It is the doctors' decision.
"I think (the health of the player) is so important, the protocol is there and our medical staff follow the protocol."
Despite that latest blow, the hosts reacted well to end the half on top with Vertonghen's replacement Moussa Sissoko driving a long-range effort wide.
Pochettino's half-time pep talk had the desired effect as Spurs dug deep into their energy reserves to raise the tempo and intensity of their display after the break.
Yet, the quality needed in the final third to get back on level terms was missing without Kane and Son.
"We arrived in the last third but we didn't find a way to create clear chances," continued Pochettino. "Always we missed the last pass or shot."
Ajax did not make the most of their chances on the break to kill the tie off, but were unfortunate when David Neres's effort back across Lloris left the French captain helpless only for the ball to rebound back off the post.
"We could have kept the ball more and played calmer and that creates opportunities," said Ten Hag.
"With for instance Neres that he didn't score that was such a pity. Nevertheless winning 1-0 in Tottenham is an amazing result.
"We know we can do a lot better next week to finish it off."
Son will be back for the trip to Amsterdam next Wednesday and Spurs will hope the South Korean can repeat his double away to Manchester City in the last eight, but Ajax are in pole position for a final against Barcelona or Liverpool come June 1 in Madrid.