Assistant coach Aitor Karanka believes Sergio Ramos' 18th-minute red card prevented Real Madrid from enjoying a far more emphatic win than the 2-0 victory they claimed over Rayo Vallecano.
Madrid had looked set to run riot in Jose Mourinho's 100th league game in charge on Sunday, after scoring twice in the opening 12 minutes through Alvaro Morata and Ramos, while going close on a number of other occasions.
However, they were halted when Ramos was sent off after picking up two soft bookings in quick succession.
The result sees Madrid remain four points behind second-placed neighbours Atletico and 16 adrift of pace-setters Barcelona in the Primera Division.
Victory was the perfect response to last week's defeat against Granada but Karanka regretted Ramos' dismissal.
He told reporters: "The party had begun beautifully for the spectator.
"It was presumably going to be a good game with us attacking but in the end it could not be. It was a shame."
Karanka also questioned the award of the two yellow cards.
The Spain international picked up his first after brushing Roberto Trashorras off the ball, and then moments later he was dismissed after a Jose Manuel Casado cross hit his hand at close range.
Karanka said: ""I think it's more of the same...and not surprising at all.
"For all it's hard to be clear because in every game actions are mistaken."
Ramos believe the sending-off was unjustified, saying: "I am hurt with the situation.
"It hurts to let my team-mates be outnumbered.
"Referees are required to interpret the play, the circumstances. I think the first yellow is unfair."