Tottenham Hotspur are still "alive" in their Champions League semi-final despite losing 1-0 at home to Ajax in the first leg, says manager Mauricio Pochettino.Donny van de Beek's goal gave the Dutch side victory over a lacklustre Spurs in north London on Tuesday."It's going to be difficult, but it's still open," said Pochettino."It's about preparing for the second leg. We will try to win. It will be tough for us, but also tough for them."History is against Spurs as only one of the 17 previous teams to lose a home first leg of a European Cup or Champions League semi-final has progressed into the final.The Premier League side paid the price for a slow start, with midfielder Van de Beek scoring the only goal on 15 minutes."I think the attitude was there, but we didn't find a way to play," said Pochettino. "We didn't show the energy we wanted to show and the way that we conceded the goal was painful. We struggled in the first half an hour."The second half was much better, we forced them to play deeper. We pressed in the way we wanted to press. The second half gave us hope for the second leg."And the Argentine took responsibility for his side's early struggle, acknowledging that a change of shape from a five-man defence to a back four aided his side."I can accept it was a mistake, the shape we used," he told BT Sport. "But there were not too many options. I am not happy - you cannot guess what happens if we play in a different way."It was the not the shape that conceded the goal. Our approach to the game was not good. I am the manager so I have responsibility."In addition, Pochettino was keen to praise his players for reaching Spurs first semi-final in Europe's premier club competition since 1962."My players are heroes to be in the situation that we are in," he said. "We need to give them full credit."