Robert Lewandowski celebrates scoring Barcelona's opening goal on Sunday.

BARCELONA — La Liga champion Barcelona celebrated a successful season with a 3-0 win at Athletic Bilbao on Sunday in its final match, with Robert Lewandowski netting twice to pass his 100 goal milestone for the club.

The veteran Polish forward, 36, reached 27 league goals for the season, finishing behind Real Madrid's Kylian Mbappe on 31.

Barcelona wrapped up a domestic treble with the Copa del Rey and Spanish Super Cup, while fourth-place Athletic also had a fine season, returning to the Champions League for the first time in 11 years.

Athletic defender Oscar de Marcos made his 570th and final appearance for the club, behind only Jose Angel Iribar, a goalkeeper who played 614 times in the 1960s and 70s, in the club's history.

Even Iribar might not have saved Lewandowski's opener, after the striker was fed by Fermin Lopez, brilliantly scooping the ball over current Bilbao goalkeeper Unai Simon to put Barca ahead and rack up the Catalans' 100th league goal of the season.

It also brought up a century of goals for Lewandowski in a Barcelona shirt since joining in 2022 from Bayern Munich, and another was soon to follow.

Three minutes later Lewandowski nodded in at the back post after a corner was flicked into his path.

"I am very happy and very proud to be part of this team, this club, it's been something amazing," Lewandowski told Barca One.

"I try to do my best, not only with goals, but my attitude on and off the pitch — and there are so many young players, we have to take care of them.

"We did something great (this season), but we know we can still do a lot (more) things."

Lewandowski missed two good chances in the second half, as Barca tried to stretch its lead and sign off in style.

In the Barcelona goal, Inaki Pena showed sharp reactions to tip the ball against the bar, after a deflection off Pau Cubarsi saw it fly toward his own net.

Barcelona's 17-year-old star Lamine Yamal forced a smart save at his near post from Simon.

The Catalans got their third when Dani Olmo won, and then converted, a penalty in stoppage time.

After the game De Marcos gave a speech to fans at the San Mames stadium and was thrown into the air by his teammates.

"I just want to thank everyone who has been there on (my) path," said the 36-year-old defender, who played 16 seasons at the club.

"Next season, I will be in the stands, as just another Athletic fan.

"And, I am sure that someone who is watching today, will be here on the pitch, representing us as Athletic."

Earlier Alexander Sorloth showed once again why he is such a dangerous option off the bench for Atletico Madrid, as he came on to score a hat-trick in under half-an-hour in a 4-0 win at Girona.

Diego Simeone's side continued its Club World Cup preparations in a dead rubber at Montilivi, with Atletico locked into third place and Girona safe from relegation.

"La Liga is over, but not the season," said Simeone, looking ahead.

"We will rest now, and from June 2, get back to training to focus on the Club World Cup."