Ibai Gomez scored the winner as newly-promoted Alaves stunned Spanish champions Barcelona with a 2-1 victory in Saturday night's La Liga clash at Camp Nou.

French defender Jeremy Mathieu cancelled out a first-half Deyverson effort to leave the two teams level early in the second period, but former Athletic Bilbao winger Gomez won it for the visitors in the 64th minute as Barcelona suffered their first league defeat of the new campaign.

Lionel Messi and Luis Suarez were both left on the bench for the home side following their international involvement in South America last week, but Neymar did return to the team after helping Brazil win gold at the Olympics last month.

Paco Alcacer and Jasper Cillessen, meanwhile, both made their debuts for the Catalan giants in a much-changed team that also included Lucas Digne, Jeremy Mathieu and Aleix Vidal.

As for Alaves, it was the same XI that shared the points with Sporting Gijon before the international break, which meant that Deyverson continued at centre-forward with support from Gomez and Edgar Mendez in the wide positions.

The first shot on target actually came from the visitors in the 14th minute of action, but Gomez's strike was always comfortable for Cillessen, who was deputising for the injured Marc-Andre ter Stegen between the sticks.

Down the other end, Barcelona had half-chances through Denis Suarez and Ivan Rakitic, but neither side had a clear opportunity of note during what was a fairly tame 20 minutes of football at Camp Nou.

Vidal had Barcelona's next half-chance in the 26th minute after finding space down the right, but Theo Hernandez was across to deflect the right-back's effort over the crossbar as Alaves continued to defend their own penalty box.

Vidal again came close 10 minutes before the break when Neymar found the Spaniard with a low free kick, but Fernando Pacheco was on hand to make a smart save.

Incredibly, it was the visitors that made the breakthrough in the 39th minute of action when full-back Kiko Femenia delivered a stunning cross into the near post and Deyverson was on hand to turn the ball past Cillessen.

Barcelona should have levelled less than two minutes later when Neymar found himself unmarked inside the Alaves box, but the Brazilian somehow headed wide from close range, before Rakitic missed the post with a powerful drive as Alaves spectacularly took a one-goal lead into the break.

Luis Enrique resisted the temptation to introduce either Messi or Luis Suarez at the break, but Barcelona were level less than one minute into the second period when Mathieu headed a corner past Pacheco from close range.

Mathieu then had a golden chance to score his second of the match two minutes later when the ball fell for the Frenchman inside the six-yard box, but he somehow fired wide of the post under little pressure.

Alaves actually had the ball in the back of the net for a second time in the 51st minute when Mendez fired home from close range, but the offside flag was raised as it remained 1-1 after an incredible start to the second period.

Messi was introduced on the hour as Enrique made his first alteration of the match and Andres Iniesta quickly followed after returning to fitness, but Luis Suarez remained on the bench following his involvement for Uruguay last week.

Suarez had to be introduced in the 66th minute, however, as Barcelona incredibly fell 2-1 behind in the 64th minute when Gomez drifted into the home side's box before finishing coolly past the reach of Cillessen.

Messi had the chance to level from a 30-yard free kick 20 minutes from time, but his effort was too high and Alaves managed to restrict the home side to very little in the 10-minute period that followed in front of a frustrated Camp Nou.

Iniesta curled one wide of Alaves's post in the 85th minute as Barcelona pressed for an equaliser and Messi had a wonderful chance late on, but the forward turned a low Digne cross wide as Alaves held on to continue their unbeaten start to the new La Liga campaign.

Next up for Barcelona is a Champions League clash with Celtic on Tuesday night, before they travel to another newly-promoted side in the shape of Leganes in the league next weekend. Alaves, meanwhile, will host Deportivo La Coruna on September 19.