Real eased to a 10th consecutive league victory, and their 14th in a row in all competitions, to cement their three-point lead over second-placed Barca who have played one game more than Jose Mourinho's side.
Champions Barca have stuttered on their travels but they maintained their superb home form against this season's surprise packages Levante, taking their record at the Nou Camp to eight wins and one draw with 39 goals scored and none conceded.
Mourinho praised his players for their solidity in defence and efficiency in attack but was reluctant to discuss the crunch game against Barca before Real's Champions League match at Ajax Amsterdam on Wednesday.
"The team is winning and we are playing well," said the Portuguese who is bidding to end his former club Barca's three-year grip on the Spanish title.
"We are winning because of our quality, the spirit of the players and our ability on the counter-attack," Mourinho told reporters.
Joint La Liga top scorer Cristiano Ronaldo added the second in the 65th, the Portuguese forward's 17th league goal of the season, before Brazil full-back Marcelo made it 3-0 in added-time after exchanging passes with France striker Karim Benzema.
Barca's 4-0 win over Rayo Vallecano on Tuesday was a game brought forward because of their participation in the Club World Cup in Japan later this month and Pep Guardiola's side produced another dominant display against Levante whose annual budget is less than 1/20th of the top two Spanish teams.
"The feeling [about the 'Clasico'] is very positive," said Barca defender Javier Mascherano. "It's going to be a spectacular match and the whole world is watching and waiting.
"We are playing a great rival who we have faced many times and we have our weapons."
