Isco struck twice in three minutes to stun Xavi's third-placed side.

But Joao Felix's stylish 90th-minute strike put Barca ahead, before Torres claimed his third to seal the success when he broke clear to fire home.

Barcelona remain eight points adrift of leaders Girona, who beat Sevilla 5-1, and seven behind second-placed Real Madrid.

Defending champions Barca had seized the upper hand when Torres tapped in a Pedri cross and were unfortunate not to be further ahead after they had two goals ruled out shortly before the break.

Torres notched his second just after the restart when he volleyed in the rebound after Lamine Yamal's shot hit the post.

Isco pulled one back in the 56th minute with a superb half volley following a mistake by keeper Inaki Pena, who flapped at a cross.

Despite an offside appeal, the former Real Madrid forward restored parity when he latched on to a ball over the top and dinked it over Pena.

Betis looked set to hold on to a battling point as the match headed towards the close, but Barca struck late twice.

Substitute Felix, on loan from Atletico Madrid, played a one-two with Torres before he curled the ball into the corner using the outside of his boot.

Torres put the gloss on the result in the second minute of added time when he finished off a counter-attack to celebrate his first La Liga hat-trick.