Barcelona maintains a four-point lead over Champions Real Madrid. However, third-placed Los Blancos, who are set to host Getafe on Sunday, have played two fewer games than Barcelona and Atletico.
Barca have now gone three league games without a victory, after a run of 11 wins in 12 prior in the top flight.
"We had a bad game, we have to look at what we're doing badly to try and improve and win games," Raphinha told Movistar. "I don't care about my goal, I care about winning, we didn't win and I'm not satisfied with the game."
ALSO READ: NBA Cup: Atlanta Hawks go past Cleveland Cavaliers again to advance, Boston Celtics beat Chicago Bulls
Barcelona wore white shorts as part of their anniversary celebrations, as they used to back at the start of their history.
They held a gala in the city on Friday night to mark the occasion, having been founded on November 29, 1899, but came undone on Saturday afternoon.
"We have to (play) like we did at the beginning of the season... it's a big disappointment today," Flick told reporters. "Today we have more than 70 percent ball possession but we're not able to score the goals -- maybe we have to change one or two things.
"We made some mistakes, but it was not the back four, it starts (with the players) in front, we have to speak about that."
The Catalans were able to name teenage starlet Lamine Yamal on the bench after recovering from an ankle problem.
Raphinha came closest to breaking the deadlock in the first half, scoring from an offside position and hitting the crossbar after being played through by Gavi.
Flick threw on Yamal at the break, hoping the winger would give Barca the advantage after an even first half.
Las Palmas took a surprise lead early in the second half when Kirian Rodriguez played in Ramirez, who drilled home from the edge of the box.
Raphinha hit back quickly for Barcelona with a thumping long-range effort, but Las Palmas were soon ahead again.
Silva ran onto Munoz's probing long ball and fired past Inaki Pena to restore the Canary Islanders' advantage with his fifth goal in eight league matches.
Former Barca goalkeeper Jasper Cillessen made several good saves and Las Palmas survived eight minutes of stoppage time.
"It was a very important win, we worked hard for it, Barca put you under a lot of pressure," midfielder Moleiro told Movistar after Las Palmas sealed their first away win at Barcelona since 1971.
Disclaimer: This story has been published from a news agency feed with minimal edits to adhere to web's style guide. The headline may have been changed to better reflect the content of the story or to make it more suitable for web audience.