Italy can also book their slot in Poland and Ukraine next year with a home win over Slovenia in the latest round of matches in the marathon and largely predictable qualifying contest.
Germany made sure of their place last Friday while none of the other top teams appear to be in any danger of missing out.
Del Bosque criticised his team's defence, whose problems are unlikely to surface against a Liechtenstein side who, despite not having a professional league in their country, have become masters at the art of spoiling.
The team from the tiny principality have picked up four points in Group I, conceded only six goals in their last five group games and have given themselves a reputation as one of Europe's most frustrating teams to break down.
Italy have dropped only two points in seven games in Group C, although Friday's 1-0 win over Faroe Islands was far from impressive.
"I barely slept after the game," said frustrated coach Cesare Prandelli. "There is much work to be done, despite our great start.
"Perhaps it's my fault as we tried out things we had been experimenting with in training too quickly. We broke into their box six times but kept on trying to pass the ball into the net without pulling the trigger."
Sweden's chances of catching the Dutch were wrecked by defeat in Hungary on Friday, although they look virtually certain to prolong the race by taking three points from a San Marino side who have shipped 44 goals in eight games without scoring.
Second-placed Montenegro's defeat in Wales on Friday has given renewed hope to Switzerland of taking the runners-up spot.
