BARCELONA, Spain -- Ernesto Valverde insisted Barcelona have not won La Liga yet despite watching his side open up an eight-point lead over second-place Atletico Madrid on Sunday.

Lionel Messi's first-half free kick -- the 600th goal of his career -- proved the difference as Spain's top two met in an entertaining game at Camp Nou.

Barca had drawn three of their last five league games, allowing Atletico to cut their advantage from 11 points to just five.

However, Atletico's hopes of taking a bigger chunk out of that lead were once again ruined by Messi, who has now scored 28 goals against Atletico and netted directly from a free kick for the third consecutive league game.

"I am very proud, above all because of how we competed," Valverde said at a news conference. "The team has always responded in these type of games, offering certain guarantees in that sense, and today was another case of that.

"It was a very important game in terms of the title race. Being eight points clear is not the same as being just two ahead. It's not definitive, obviously, but it's a step forward. Let's see what the future holds."

Midfielder Sergio Busquets also played down the significance of the win as Barca target a third league title in four years.

"The team gave everything," he said. "We were better. We had possession, chances and Leo's goal was sensational. This is how you win La Liga: suffering and winning against the best, and today, we have beaten the team second in the table.

"But it's not over. There are still tough games between now and the end of the season. It's true we have the head-to-head advantage over Atletico now, too, but we will take things game by game."

Barca's win extended their unbeaten start to the La Liga campaign to 27 games, while their unbeaten run in the league now stretches back 34 matches encompassing last season.

Lionel Messi scored his 600th career goal against Atletico Madrid. PAU BARRENA/AFP/Getty Images

However, a first-half injury to Andres Iniesta put a slight downer on the win against Atletico.

Iniesta will undergo tests on a hamstring injury on Monday at the club's training ground, but early reports in the Catalan press suggest he will be sidelined for the next month, ruling him out of the Champions League game against Chelsea on March 14.

"Iniesta is a unique player, a little like Messi, so it's difficult to find a player who can replace him," Valverde said when asked how he will substitute the club captain in the coming weeks.

"He is unique in the world in terms of the characteristics he has. We will have to see the extent of the injury. He carried on playing at first so we thought it wasn't too bad, but we're not sure. ... He was playing incredibly."

Gerard Pique also looked set to go off later in the second half as he continues to struggle with a knee problem, although he recovered to finish the game.

"Pique has an injury which allows him to keep playing," Valverde said. "It's not a big problem and with two or three weeks' [rest], he could be fine.

"He can play. We're risking him. It depends a little on if he takes a knock in the injured area. For the moment, it's not gone badly, so we will keep on going with him."