Real thumped Real Zaragoza 6-0 just hours after Barca defeated Estudiantes to win their sixth trophy of the year.
"It is difficult to do what they did," said Pellegrini.
"We are within two points of them, having been to the five toughest grounds. I believe they have more difficult trips to come.
"Their great performance lends even more merit to ours, because we are keeping up with them."