Spurs lie seventh in the standings and eight points behind leaders Arsenal close to the halfway point of a season in which they were expected to challenge for the title.
Portuguese manager Villas-Boas, whose side appeared to have got back on track after a 6-0 thrashing by Manchester City on November 24, has come under increasing pressure as his new-look team get to grips with life after Gareth Bale.
And this latest blow has led to speculation that he may be the next Premier League boss to face the chop.
While he refused to comment on his own future, Villas-Boas admitted he and his team need to do better in the league.
“I assume the responsibility of the failure. We have to bounce back again as we did after City. In the Premier League things are not going as expected,” he said afterwards.
“Obviously we want to put things right. This was another great opportunity for us to get back on track in the Premier League.
“I don’t need to convince anybody that I can turn things around. Our results are magnificent in other competitions but not in the Premier League.
“Regarding my position it is not me who decided. It is up to me to make things better. We have the best record of shots in the Premier League but today we were unable to do this.”
Villas-Boas insisted that his charges have what it takes to change their fortunes, pointing to their good record in other competitions, particularly in Europe, where they won all six of their Europa League Group K matches, scoring 15 and conceding twice.
“We have to play a quarter-final with West Ham in the League Cup, and we await the draw for the last 32 in the Europa League,” he added.
“Our ambition to win trophies is still the same and our ambition to qualify for the Champions League is the same.”