Ronald Koeman believes Barcelona played their best football in "years" during the opening hour of their first LaLiga game since Lionel Messi's exit as they saw off Real Sociedad 4-2.

Martin Braithwaite's brace after Gerard Pique had opened the scoring gave Barca a three-goal advantage with 59 minutes played in Sunday's contest at Camp Nou.

Julen Lobete and Mikel Oyarzabal scored quickfire goals to set up a nervy conclusion to the game, but Sergi Roberto struck in injury time to seal a deserved win for the home side.

It was the perfect way for the Catalan giants to put the shock of losing their all-time leading goalscorer Messi to Paris Saint-Germain on a free contract this week behind them.

And while Koeman would prefer to still have Messi in his squad, the Dutchman feels Barca proved there is life without their former captain as they outclassed La Real.

"We know that we are good with the ball, but we have worked hard on pressing and to do so with everyone," Koeman said during his post-match news conference. 

"We have to be more collective than before. For me, the team in the first half hour was the best Barca in years. It is the path we want to follow.

"I would like to have Messi in the team. Of course we don't have the player who decides games on his own, but this is more about the collective now.

"We have to create opportunities to score. Today we scored four so it's fine."

Pique got the ball rolling for Barcelona with his 19th-minute opener, heading in a pinpoint free-kick sent in by Memphis Depay on his competitive debut for the club.

Depay, Eric Garcia and Rey Manaj could only be registered by Barca on Saturday after Pique accepted a substantial pay cut to ensure they met LaLiga's salary cap limit.

Pique celebrated his goal by kissing the Barcelona crest on his shirt and Koeman hailed the long-serving defender for putting the team first.

"For me, Pique was also the team leader last year," Koeman said. "Due to injuries he couldn't play as much as he would have liked. He has been exemplary for all the Catalans."

Braithwaite was Barcelona's star performer in their opening match of the 2021-22 campaign with his two goals, which makes him the first Danish player to score a brace in LaLiga this century.

His double came from an expected goals return of 0.89 and Koeman expects the 30-year-old to play an important role this campaign, despite being heavily linked with a move away from Camp Nou.

"I have always said that he is a great example of a professional soccer player," Koeman said. "He always works for the team and he has improved his game – not only because of the goals. 

"He helps us in many areas. He also has speed and always he is very difficult to defend against. I am delighted to have players like him."

Barcelona are now unbeaten in their last 11 league games against Real Sociedad in LaLiga, but tougher tests lie in wait with Sevilla and Atletico Madrid to come in their next seven games.

Following a period of doom and gloom, Koeman is hoping for a positive future with returning supporters fully behind their side.

"We know that the season is very long and many things can happen," Koeman added. "If the fans see a team with enthusiasm, that tries to do things well, with a positive attitude, that always helps. 

"We need the fans. We have to leave them happy and I think they have gone home happy today."