Real Madrid went top with a 1-0 win at Real Sociedad before being replaced by Atletico Madrid after they beat Rayo Vallecano 1-0.
But Barca held their nerve to overcome Betis, who had Heiko Westermann sent off for two bookings, with goals from Ivan Rakitic and Luis Suarez.
Each team has two matches remaining.
Relive the win that took Barcelona back to the top of the table.
Defending champions Barcelona had scored 14 goals in winning their previous two league games.
But they found it difficult to break down a Betis side who played with 10 men from the 35th minute after defender Westermann had tripped Rakitic to earn his second caution in the space of eight minutes.
The opening goal came five minutes into the second half when a Lionel Messi ball into the penalty area caused confusion between defender German Pezzella and goalkeeper Antonio Adan, and midfielder Rakitic was left with a simple tap-in for his 10th goal of the season.
The second goal did not come until nine minutes from time when Messi played through a perfect pass for Suarez to slot home his 54th goal of the season.
Barcelona keeper Claudio Bravo came off late on with a calf strain and will have further tests on the injury on Sunday.
Barcelona coach Luis Enrique: "It's a very competitive league and I think the three candidates are strong. No-one will slip up, we depend on ourselves.
"There is less to go (now). I am sure against Espanyol, Camp Nou will be packed to the rafters."

Len McCluskey joined Unite members from the Oxford Bus Company on the picket line earlier, and warned seven other bus depots run by the Go Ahead Group could be affected.
Drivers have walked out on two separate days angry that they were only paid for three bank holidays over Christmas.
Oxford Bus Company said its drivers were among the highest paid anywhere.
'Incredible resolution'
Mr McCluskey warned that unless the issue was resolved, bus services in London and other parts of the country could also expect industrial action.
He said: "I sincerely hope that the Oxford Bus Company pays heed to the incredible resolution of Unite's members.
"They are in no mood to roll over, and they know that they have the full support of their union in their corner.
"Unless the company restores facility time and starts treating our members with respect I will have no option but to take this dispute to every Go Ahead depot in the country."
But Phil Southall, the managing director of Oxford Bus Company, said it was continuing to run about 90% of services.
He added: "This is purely a local issue to Oxford about the Christmas and New Year bank holidays.
"We were willing to agree to suspend any legal action, reinstate the recognition agreement and the stand down time at Unite's request if strike action was called off and no further dates announced.
"It is becoming clearer that this strike is about Unite the union and not about our drivers' and engineers' best interests."
The Go Ahead Group says its operations include eight regional bus companies, one of which is in London, where it provides about 24% of services on behalf of Transport for London.
Barcelona beat 10-man Real Betis 2-0 to regain top spot in La Liga at the end of a day that saw all three title rivals spend time as leaders.
[NEXT_CONCEPT]
The leader of England's biggest union has warned that a strike by bus drivers in Oxford over pay could spread.