Christian Eriksen admitted Tottenham were well below their best as Ajax seized the initiative with a 1-0 win in their Champions League semi-final first leg on Tuesday.

Mauricio Pochettino's side were out-classed in the first half at the Tottenham Hotspur Stadium and fell behind to Donny van de Beek's 15th minute strike.

Tottenham were slightly better in the second half, but Ajax remained the more cohesive team and could have added a second goal when David Neres hit a post in the closing stages.

Denmark playmaker Eriksen was one of many Tottenham stars who failed to shine on the night and he conceded it was far from their best display.

"We were under-par, we didn't play our best at all. In the first 20 minutes, we were ball-watchers. We need to change it up a lot for the next game," Eriksen told BT Sport.

"We made them look a lot better. They are a good side, but we helped them along the way. It was our fault. We were better in the second half.

"No one wanted to play the first half we did. Everyone knew we didn't compete. We still lost, but we were better in the second half."

Tottenham's cause wasn't helped by the absence of injured leading scorer Harry Kane and suspended forward Son Heung-min.

But Eriksen insisted Tottenham shouldn't use that as an excuse.

"We can't keep talking about injured players. In a semi-final it doesn't matter who plays, we have to step up," he said.

"At the start, the system didn't matter. The change gave us a different way to press, to play more direct. But we were still far from where we know we can be."

Only one of the 17 previous teams to lose the first leg at home in a European Cup semi-final has progressed into the final -- ironically Ajax in 1995-96.

Tottenham will have Son back from his ban for the second leg and Eriksen said it could have been much worse for the side going into the decisive return in Amsterdam next week.

"We're lucky they hit the post and hopefully we can turns things around in Amsterdam," he added.