Mourinho demands better from Real
Gonzalo Higuain and Angel di Maria netted first-half goals before Michael Essien and Luka Modric ensured the defending champions made it five La Liga games without defeat.
With Valencia ending Atletico Madrid's unbeaten start to the season, Real are within five points of their city rivals, but Mourinho stressed the importance of an improved performance in their next league match.
"It was not our best game today and we can and we must play better," he said.
"But the important thing for us is to win and to also win calmly.
"We have to play better than we did today if we are going to get results."
Modric scored his first goal since moving from English Premier League club Tottenham in the off-season, finding the back of the net from the edge of the box deep into injury time.
And Mourinho was full of praise for the Croatian international.
"I really like Luke Modric since he joined," the Portuguese tactician said. "He works well and he is adapting very well.
"Playing in the Premier League and playing in the Spanish league are very different.
"And playing in Tottenham is as well different than playing for Real Madrid but he is a great player."