The Argentina international is refusing to read too much into his side's second consecutive defeat, but admitted it must do better.
The Blaugrana lost their unbeaten record in the Primera Division following Iker Muniain's winner, yet Mascherano remains optimistic and is determined to bounce back in Friday's Copa del Rey game against Cartagena.
"It hurts to be beaten. Nobody likes to lose, but let's not forget we are still leaders," Mascherano told the official Barca website. "We have to win the games that are left this year, beginning with the matches against Cartagena and Villarreal."
However, the defender then went on to admit that Barcelona will have to improve in order to get back to winning ways.
"We were more intense than against Ajax [in the Champions League], but that wasn't enough to give us the win. We have to put right the things we have done badly and look at ourselves. We've done things right as well, though."
Barcelona sits first in La Liga level on points with Atletico Madrid.