With French winger Ousmane Dembele out injured for the next few weeks, Raphinha grabbed his chance to prove himself.
Dembele’s superb form had limited the Brazilian’s minutes since his move from Leeds United last summer.
Raphinha put Barcelona ahead in the 65th minute and Lewandowski, back after a three-match league ban, netted the second with 10 minutes to go.
Jules Kounde scored an unfortunate own goal to give Betis a fighting chance of a point in the final stages but Barcelona held out for the win.
“I think we had a good game, our play was very good, excellent I would say,” Barca coach Xavi Hernandez told Movistar.
“We played a great game at a very difficult place to come. I’m very happy not just for the result but for how we played, we’ve improved a lot from the Girona game.”
Barcelona had won their previous three league games 1-0, including against Catalan rivals Girona last weekend in a flat performance, but were operating on a higher level in Seville.
Betis started well in front of their boisterous support, with Alejandro Balde doing well to block Luiz Henrique’s effort in the opening exchanges.
At the other end Lewandowski headed wide, while Pedri could not find a finish when racing through on goal.
Raphinha had a goal ruled out for a clear offside and Kounde flung himself in the way of Sergio Canales’s strike.
Betis goalkeeper Rui Silva denied Pedri either side of half-time as the Spain international tried to continue his own goalscoring form after netting the winner in Girona.
– Eight points clear –
Raphinha appealed unsuccessfully for a penalty after a tangle with Abner Vinicius in the area, but the Brazilian’s complaints soon turned to celebrations.
Frenkie de Jong cleverly fed Balde from a quick free-kick and the young left-back slid a ball across the face of goal for Raphinha to tap home.
“It’s about attitude, competitiveness, desire, faith, our hopes are huge,” said Xavi when asked about De Jong’s quick thinking.
“We are at a good moment with this, we have confidence and the morale to achieve success. That matters, too, it’s about competing well.”
La Liga’s top scorer Lewandowski’s return was largely a frustrating one for the striker, having a shot blocked after Sergio Busquets set him up, while his touch was unusually clunky.
However the Polish international finished clinically after Ronald Araujo headed down to him, to net his 14th league goal of the season and 23rd across all competitions.
Substitute Ansu Fati headed wide from another fine Balde cross, before Kounde accidentally chested a ball into his own net past the outstretched arm of Marc-Andre ter Stegen, setting up a nervy finale.
Barcelona survived to round off the first half of their league campaign with a victory, aiming to win the title for the first time since 2019.
Betis, sixth, had William Carvalho sent off after the full-time whistle for protesting some of the refereeing decisions.
The Andalusians sit three points behind Atletico Madrid in fourth.
“Against Barca the games are always like this, it’s hard to take the ball off them, they are capable of pushing you back and keeping you in your own half,” Betis forward Borja Iglesias told Movistar.
“Until their goal we were doing well, from there it was a different game.”