The champions were largely outplayed by their city rivals and Garcia kept them afloat in the derby clash against his former side before substitute Olmo curled home in the 86th minute.

Fermin Lopez created Olmo's goal before laying the second on a plate for another replacement, Lewandowski, as Barca claimed a ninth consecutive league victory and ended Espanyol's own run of five wins in a row.

"We didn't deserve it, I'll be honest, but in the end the quality we brought on the pitch after the changes decided the game," said Flick.

"First of all I have to say thank you to Joan Garcia because he played unbelievably. He's one of the best goalkeepers in the world."

Manolo Gonzalez's side, fifth, could have claimed at least a point from a typically spiky battle at the RCDE Stadium, before Barca's substitutes decided the game.

Second-placed Real Madrid host Real Betis on Sunday.

Espanyol fans gave Garcia a particularly hostile reception, after he became their first player to leave for Barca in more than 30 years in the summer.

The hosts hung huge safety nets behind the goals to try and protect Barca's stopper, who was whistled throughout, from projectiles while fans waved banners with pictures of rats at him.

Amid the ire, Garcia made two vital first half interventions that sent the teams in level at the interval.

"Joan is incredible, a great goalkeeper. Playing against his old fans, he had a great game and got a clean sheet," Olmo told Movistar.

"He will give us a lot -- he's giving us that and he will give us so much more too, I'm sure."

- Subs settle game -

There were few clear chances in a tense first half and the best openings fell to Espanyol.

Striker Roberto Fernandez got in behind Barca's high line, one-on-one, but Garcia blocked his shot and then improvised brilliantly by shoving team-mate Gerard Martin into the way of Pere Milla's follow-up.

Then Garcia produced a stunning save to tip away Milla's header which seemed destined for the back of his net.

The goalkeeper's excellent performances last season helped Espanyol stay in the top flight but when the champions came calling, he made the rarely-taken move across the city.

Barcelona's goalkeeper was called into action again as Fernandez burst through on goal in the second half, with Garcia pushing the ball to safety as the forward tried to round him.

Kounde cleared off the line and Garcia tipped Fernandez's near-post drive away as Espanyol continued to harry Flick's side.

Barcelona's first clear chance came in the 70th minute, falling to Eric Garcia from point-blank range, but  Marko Dmitrovic, at full stretch, made an astonishing save to keep the scores level.

Eventually three of Flick's substitutes combined to settle the game in Barca's favour.

Lopez drove forward and found Olmo, who whipped a shot into the top right corner to break the deadlock. It was Olmo's first appearance for over a month, following a dislocated shoulder.

Lewandowski dinked home the second in the 90th minute after another fine Lopez charge into the area to complete Barca's smash-and-grab success.

"I don't celebrate the first 80 minutes, how we played," admitted Flick.

"But in the end we scored the two goals, got the three points and this is a massive message to La Liga and very important."

Elsewhere Villarreal maintained the pressure on La Liga's top two with a 3-1 win at Elche on Saturday to go provisionally third. Atletico Madrid, fourth, visit Real Sociedad on Sunday.

A defeat by Barcelona before the winter break was a setback for Marcelino Garcia Toral's Villarreal but they started the new year with a convincing triumph at the Martinez Valero stadium.

Alberto Moleiro and Georges Mikautadze fired the visitors into a comfortable lead inside 13 minutes with clinical finishes.

Martim Neto pulled one back for Elche from the edge of the box, but Alfonso Pedraza wrapped up Villarreal's win late on by slipping in behind and maintaining his composure to beat Inaki Pena.