Raphinha extends Barca's Liga lead, Atletico bounce back
Atletico Madrid, fourth, returned to winning ways with a 2-1 victory over Valencia sealed by a fine Antoine Griezmann strike, while Espanyol, fifth, continued their strong start with a 1-0 win at Getafe.
Barcelona's Brazilian winger Raphinha broke the deadlock after 70 minutes with a fizzing strike from the edge of the box, and added a second late on to earn Barca their seventh-straight top flight win.
Second place Real Madrid visit Alaves on Sunday, aiming to cut the gap on the champions back down to four points.
Barca lacked their usual sparkle but ground out their victory, keeping a first clean sheet in six matches across all competitions.
They also recorded a fifth victory in five games at their partially reopened Camp Nou home.
"Raphinha is very important. He scored two goals and is a key player. He defends and attacks -- he's very important for us," said Flick.
"Maybe we didn't have many chances, but we scored two goals and got the three points."
Ferran Torres might have sent Barca ahead early on but hooked high over the bar from Lamine Yamal's dangerous cross.
Yamal had a couple of drives beaten away in a mostly frustrating first-half for both the teenager and for Barca.
Torres headed home from Marcus Rashford's cross but the goal was disallowed for an offside in the build-up.
The Spain international sent an acrobatic overhead effort inches wide, and Barca goalkeeper Joan Garcia denied Ante Budimir with a fine save before the break.
Barca were having trouble breaking Osasuna down but found a way through when the excellent Pedri roamed forward and found Raphinha on the edge of the box to slam a shot into the bottom right corner.
Osasuna's Jorge Herrando, who was sent off on his debut for the club at the old Camp Nou in 2023, had a strike ruled out after Alejandro Catena collided with Barca goalkeeper Garcia.
Moments later, Raphinha tapped home at the back post after Alejandro Catena deflected Jules Kounde's cross into the Brazilian's path with four minutes remaining.
Raphinha, who started the match out of position in a central attacking midfield role, was one of the club's key players last season as they won a domestic treble and, after a spell out injured, has made an impact on his return.
"We've got a lot of good players and Rapha, or whoever else plays inside, in the end they give us a lot of solutions in that position," said Barca defender Gerard Martin.
Atletico back on track
Goals by captain Koke and Griezmann brought Diego Simeone's fourth-placed Atletico Madrid some respite, although they trail Barca by nine points.
Atletico had muscled their way back into the Spanish title race after a slow start to the season, before suffering damaging consecutive Liga defeats by Barca and Athletic Bilbao at the start of December.
They followed up a Champions League victory at PSV in midweek with a solid display at their Metropolitano stadium against Los Che.
"It was hard for us to find our rhythm, and in the end it was the substitutes who gave that spark and that speed, so that we could win today," Griezmann, brought on in the second half, told DAZN.
Valencia began well, Hugo Duro hitting the crossbar, but were undone by a scramble at a corner. Goalkeeper Julen Agirrezabala repelled one effort but was unable to do anything as Koke slid home the rebound.
Valencia, 16th, pulled level soon after the hour, with Beltran's blast from distance catching out Atletico goalkeeper Jan Oblak.
Simeone's side won it through Griezmann, who plucked Marc Pubill's long ball out of the sky with a raised left leg, read the ball's bounce and lashed it past Agirrezabala for his fifth league goal.
Manolo Gonzalez's Espanyol kept the pressure on behind Atletico with Leandro Cabrera's header early in the second half helping his side down Getafe and bolster their hopes of European football next season.
Third-place Villarreal's game at Levante is likely to be postponed because of storms forecast in the region, with the Valencia council requesting La Liga suspend the match.