Barcelona beat La Liga champions Cadiz 1-0 in their second home defeat in four days.
Perez missed a brilliant first-half chance 12 yards out, but the former Arsenal striker only returned home 47 minutes later.
Jeremias Ledesma has been linked with a move away from Stamford Bridge, where he has been linked with a move away from Stamford Bridge.
Barca's slim La Liga title hopes have been dashed since Thursday's exit from Eintracht Frankfurt in the Europa League, just five points behind fifth-placed Real Betis.
Some fans went on strike at the Nou Camp. Barca saved Ledesma twice with Ousmane Dembele and Ferran Torres.
Cadiz soon found the back of the net 27 minutes after settling in, and Perez crossed from the edge of the box and fired in from close range.
Dumbley fired a powerful shot into the back of the net, with Perez giving Barcelona the chance to make a resounding success after Perez failed to save Marc Andrea Stegan from close range.
Ledesma blocked Dumbley again 20 minutes later, but Barca were lucky to miss out on opportunities from Alex Fernandez and Rubin Sobrino.
Ledesma rejected Luuk de Jong, avoiding Eric Garcia's goal, and Barca responded with a disappointing defeat to Pierre-Emerick Aubameyang's volleyball before making his best save before the match.
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Xavi Hernandez's side have won seven consecutive La Liga games this season, and for the first time since January 2019, Ernesto Valverde has won eight consecutive league games.
However, Cadiz, who was threatened with relegation, punished the home side for their first win at La Liga.
Cadiz became Barca's Bogey team.
It was Cadiz's first La Liga away win at Barca, but the Andalusians have not lost in their last four games against the Blaugrana.
Perez, meanwhile, scored four league goals against Cadiz against Barcelona and just six against Valencia. The three strikes came to Kannu.
Barca missed two defenses.
Barca created an unmotivated attack, but missed out on first-choice defenders Ronald Araujo and Gerard Pique.
Eric Garcia is unbeaten in his last three games with Clement Lenglet, and neither of them has been able to stop Perez.
Key Opta Facts
For the first time since April 2003, Barca have lost their first home game in a row in all competitions - Barca have won just nine clean sheets in La Liga after 31 games this season. The worst number in the 21st century is 10 in 2012-13. Dumbledore has competed seven times this season, his highest record in a single event (seven times against Lenarez in the Copa del Rey). Barca have scored 32 goals in 31 La Liga appearances, the worst record at this stage after 33 assists in the 2012-13 season. Ledesma is the first goalkeeper in La Liga this season to score six goals without conceding a goal.
What is the next one?
Barcelona travel to Real Sociedad in La Liga on Thursday and return to action earlier in the day when Cadiz host Atletico Bio.