Lionel Messi opened the scoring from the penalty spot after 15 minutes and Jordi Figueras, who had conceded the spot-kick, doubled Barca's lead with an own goal midway through the second half.
Betis striker Ruben Castro quickly pulled one back for the visitors but Messi struck again in the 85th minute, reacting quickly to having a penalty saved to send the ball in on the rebound and seal the three points.
Before kick off, fans showed their opposition to the FIFA-imposed transfer ban on Barcelona - a punishment for signing under-age overseas players to the club's famed academy La Masia - by unfurling a huge, eye-catching banner with the message "La Masia shall not be touched".
La Masia graduate Xavi Hernandez showed great technique to hit a half-volley towards goal from the edge of the area 11 minutes in, but former Real Madrid goalkeeper Antonio Adan got across to make the save.
The hosts got a breakthrough when Alexis teased the Betis defence in the area and was eventually felled by Figueras. Messi coolly rolled the ball the other side of Adan to give Barca the lead and score his fourth penalty in as many league games.
The Catalans nearly doubled their advantage with a marvellous team move which originated from a sweeping ball from Messi to Adriano on the left, but neither Pedro nor Dani Alves were able to reach the cross towards the back post.
Messi almost scored a sensational goal before the break, floating past several Betis defenders and firing a shot off the outside of the post.
Then it was Xavi's turn to hit the woodwork, the Spain midfielder clipping the crossbar from a free-kick just a few minutes into the second half.
Barca struggled to create many openings after Xavi's miss and had a few hairy moments at the other end, such as when Cedrick Mabwati shot high over the bar from inside the area and when Alfred N'Diaye slid in to force Jose Manuel Pinto to tip his shot over the bar.
Alexis should have sealed the points on 65 minutes when he received a through ball by Iniesta in the area, but the Chilean lost control as he tried to round a Betis defender rather than shoot on goal.
But Barca got that important second goal a moment later, Figueras completing an embarrassing afternoon by sending Adriano's cross into his own net 20 yards out.
However, Betis got back into the game in the next minute, Castro gobbling up the loose ball on the edge of the area and evading tackles from Barca players to knock the ball into the net and ensure a nervy finish for Barca.
Messi and Alexis failed to take opportunities to put those nerves to rest - the Argentinian was unable to keep his first time shot under the bar and then the Chilean blasted over at the near post with just Adan to beat.
Sunderland loanee N'Diaye caused problems for the Barca defence by putting his weight about at the other end but could not get a shot away, and the game was wrapped up with six minutes remaining when the hosts were awarded a second penalty, Betis captain Antonio Amaya penalised for blocking a cross by Neymar with his hand.
Messi's spot-kick was saved by Adan, but the Argentinian reacted quickly to knock in the rebound and score his 10th goal in five league games, totalling 25 for the season.