MADRID, Aug 21 (Reuters) - Vicente del Bosque began his reign as Spanish coach with his side's 3-0 win over Denmark but said there was plenty of room for improvement for the European champions ahead of next month's World Cup qualifiers. 'We started badly, we were slow and over cautious,' the former Real Madrid boss told reporters after the friendly in Copenhagen. 'Denmark were better than us in the first half but we reacted well and ended up playing a good game against high level opposition.' Spain were in muted form in the opening minutes of a match that was overshadowed by news that over 150 people had been killed in an air crash at the Madrid airport earlier in the day. Denmark had several chances to take the lead after lapses in the Spanish defence, but the visitors gradually warmed to the task and saw off the home side with three classy second half goals. Midfielder Xabi Alonso fired home the first after some great work by Fernando Torres who flicked the ball back over the head of a defender before providing a neat assist for his Liverpool team mate. Playmaker Xavi cracked in the second with a crisp shot from the edge of the area and Alonso wrapped up with a confident volleyed finish. 'We have to recognise that if it hadn't been for (defender Carles) Puyol and (goalkeeper Iker) Casillas we would have conceded at least one goal, but the players' confidence and skill allowed us to overcome the poor start and win the game,' said Del Bosque. 'We've got two World Cup qualifiers coming up and we have to get things right because we can't afford to make any mistakes. We are the favourites to win but we can't slip up especially when we play at home.' Double goalscorer Alonso said that the team would try to keep faith with the style of play that had brought them success at Euro 2008. 'This system worked at the European championship. With the players we have in the team we need to keep playing the same way and it worked against Denmark especially in the second half,' he told reporters. Fellow midfielder David Silva stressed that the team would not be resting on its laurels after its Euro 2008 triumph. 'There are a lot of young players in this team and we haven't fulfilled our potential yet,' he said. 'We want to continue the same progress we made at Euro 2008 and with Del Bosque it looks as though we are going to maintain the momentum.' Spain begin their World Cup qualification campaign with matches at home to Bosnia and Armenia on Sept. 6 and 10. Estonia, Belgium and Turkey are their other opponents in Group 5.