Lewandowski captained Barca on Sunday as he appeared in front of the Catalan faithful for the final time, with two goals from Raphinha and one from Joao Cancelo ensuring a fitting send-off.
The 37-year-old, who has scored 119 goals since arriving from Bayern Munich in 2022, was substituted late on but returned for a lengthy tribute at the close, with the hosts having set a record by making it a maximum 19 wins in front of their own supporters.
Rivals Real Madrid also picked up three points with a 1-0 win at Sevilla, Vinicius Jr with the only goal of the game in the 15th minute.
Celta Vigo guaranteed European football next season with a 1-1 draw at Athletic Bilbao, with their goal difference strong enough to mean they will almost certainly be in the Europa League.
Getafe hold seventh, and the Europa Conference spot, by a point after losing 1-0 at Elche, who secured three huge points to go two clear of the relegation zone thanks to Victor Chust's winner.
Valencia scored twice in the closing seconds despite being down to 10 men to beat Real Sociedad 3-2 and keep their chances of taking Conference football with a seventh-placed finish. Rayo Vallecano defeated Villarreal 2-0 to retain their own chance of snatching a European place.
Mallorca lost 2-0 to fellow strugglers Levante, both sides down to 10 men by the time Kervin Arriaga finished things off in the 87th minute after Carlos Espi's opener. The result took Levante two points clear after Girona were downed 1-0 by Ademola Lookman's goal for Atletico Madrid.
Having gone 143 days without a win, Espanyol ensured their survival with their second win in a week, with Kike Garcia grabbing the decider in a 2-1 defeat of Osasuna. Already-relegated Real Oviedo lost 1-0 at Alaves.
In Serie A, Napoli nailed down second place behind Inter Milan and the Champions League spot that goes with it. Scott McTominay kicked off the scoring in a 3-0 win over relegated Pisa.
Juventus dropped from third to sixth after going down 2-0 at home to Fiorentina and may now have to settle for the Europa League. Their slip allowed both AC Milan, Roma and Como to overtake them.
Milan beat Genoa 2-1, Roma claimed a 2-0 win against Lazio in a capital city derby that saw both teams finish with 10 men and Gianluca Mancini score twice. Como edged Parma 1-0.
Jamie Vardy earned Cremonese a 1-0 win over Udinese, but Nikola Stulic struck deep into stoppage time to hand Lecce a dramatic 3-2 victory at Sassuolo to retain their one-point advantage in the battle at the bottom.
In Ligue 1, France star Ousmane Dembele limped off injured less than two weeks before the Champions League final as Paris St Germain suffered a last-gasp 2-1 loss at neighbours Paris FC.
Bradley Barcola gave Luis Enrique's side the lead early in the second half before Alimami Gory's double, including a winner deep into added time, snatched a shock derby victory for the hosts.
Marseille pipped Rennes to Europa League football next term, leapfrogging their opponents with a 3-1 victory in their season-ending head-to-head.
Pierre-Emile Hojbjerg's opener after just 90 seconds put Habib Beye's side in charge.
Rookie goalkeeper Mathys Silistrie gifted a second to Amine Gouiri and Pierre-Emerick Aubameyang's third rendered Esteban Lepaul's late effort a mere consolation on their way to the Conference League.
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