Saturday's 2-1 victory over last season's runners-up Liverpool ensured Chelsea will go into the international break four points clear of Southampton at the top of the table.
Meanwhile, their other title rivals Manchester City, Arsenal and Manchester United have all stuttered this term, with Manuel Pellegrini's side - the closest of that trio - eight points back after being held by QPR at the weekend.
And Azpilicueta believes Chelsea's close-season acquisitions have helped improve their squad both technically and mentally, which gives them a clear advantage.
"I think we are stronger mentally now," said the Spain international. "The players who came have given us another dimension as well.
"I think you saw that [against Liverpool]. When the team was losing we were still really strong mentally.
"The whole squad know we have to fight together. Some players have more talent, some score goals, and sometimes we have to defend for them - but the main thing is we do it all as a team.
"Over the last few games maybe we haven't played our best football and the scores have been tight but over the whole season you know that everyone can't keep playing very well and winning easy.
"Last year we were so close to winning the title and this year we know it will be tough but that's what we want.
"We will see in May. We're on top of the table but that's a long way off, but we want as few problems as possible up to then."
