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

Barcelona wrapped up a domestic treble with Copa del Rey and Spanish Super Cups wins, while fourth-place Athletic also had a fine season and returned 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 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, 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 their lead and sign off in style.

In the Barcelona goal, Inaki Pena showed sharp reactions to tip a ball against the bar as a Pau Cubarsi deflection headed towards his own goal.

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 and was thrown into the air by his team-mates.

"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."

- Sorloth super-sub -

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 their Club World Cup preparations in a dead rubber league match at Montilivi, with Atletico locked into third place and Girona safe from relegation.

Introduced in the 62nd minute for Antoine Griezmann, Sorloth broke the deadlock after 68 minutes.

Clement Lenglet extended Atletico's lead before Sorloth struck two more late on to reach 20 La Liga goals, 12 of those as a substitute.

Sorloth hit four goals earlier this month against Real Sociedad, with the first three of those scored by the 11th minute, making it the earliest hat-trick in La Liga history.

"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."