Madrid looked to be cruising to their first league success since 2008 after winning 11 consecutive matches, but disappointing 1-1 draws in their last two outings against Malaga and Villarreal has offered Barcelona renewed hope of retaining their crown.
Barca had trailed by 10 points heading into last weekend's fixtures but the gap is now six - and it could be three by the time Jose Mourinho's men kick-off against Sociedad as the defending champions face Real Mallorca in Saturday's early kick-off.
Nevertheless, Marcelo insists his side are still in an enviable position at the top of the standings.
The Brazil international also dismissed suggestions Madrid, who saw Mourinho sent to the stands and Sergio Ramos and Mesut Ozil both red-carded in the three minutes after conceding an 83rd-minute equaliser to Villarreal, were feeling the pressure.
"Any team would like to be six points ahead. We need to be calm. We are well. We didn't win here (at Villarreal), but the spirit in the team is good," Marcelo, who was the only person from Madrid to speak to the press following the match, told La Sexta television channel.
The full-back was also asked about the performance of the referee at El Madrigal, to which he replied: "You've seen what you've seen. At times the referees hurt us too much, but we have to keep our heads up and carry on forward.
"We have to do our own jobs."
Barca have taken full advantage of Madrid's slip-ups this week with victories over Sevilla and Granada to take their winning streak to six in La Liga.
Lionel Messi became Barca's all-time leading scorer with his eighth hat-trick of the season during Tuesday's 5-3 win over Granada, taking him two past Cesar Rodriguez's previous mark of 232 official goals.
Barca midfielder Thiago said of the Argentina superstar: "Messi is unique. He is a player who has made history, is making history and will make history."
Aside from the matches involving Barca and Madrid, Saturday night's other fixture will see third-placed Valencia go to Getafe.
Valencia suffered a shock home defeat to nine-man Real Zaragoza last night, but coach Unai Emery remains confident of a fop-four finish.
He said: "We've got our objectives set and I'm sure we will achieve them. I have faith, strength, and we are going to do it. Next season Valencia will play in the Champions League."
Rock-bottom Zaragoza will aim to build on that valuable win when they host Atletico Madrid on Sunday, where a win could see them climb above second-bottom Sporting Gijon, who face a tough trip to Athletic Bilbao.
The other team in the relegation zone, Racing Santander, are at Real Betis.
In this weekend's other games, the battle for European places could hot up in the clashes between in-form Levante and Osasuna, as well as Espanyol and Malaga, while Rayo Vallecano host Villarreal.
On Monday, Granada face Andalusian rivals Sevilla.
Saturday's La Liga Fixtures
Sunday's La Liga Fixtures
Monday's La Liga Fixtures
Granada vs Sevilla