The five-time World Player of the Year struck either side of Carlos Castro's well-worked equaliser in a three-goal burst in five first-half minutes.
Luis Suarez missed a second-half penalty days after famously converting Messi's pass from a spot-kick against Celta Vigo, but made amends with a brilliant finish for Barca's third.
Atletico Madrid are Barca's closest challengers with Real Madrid a further point adrift in third.
Messi, Suarez 'penalty of the century' rehearsed, reveals Neymar
"We are where we want to be and depend on ourselves," said Barca boss Luis Enrique.
"I think we controlled the game and created a lot of clear chances despite the problems that are always caused when a team plays a lot of men behind the ball."
The match had been postponed due to Barcelona's commitments in the Club World Cup in December and, with a huge clash against fellow strugglers Real Betis to come on Saturday, Sporting boss and former Barca defender Abelardo Fernandez made nine changes to his side from the team that started Friday's 2-2 draw with Rayo Vallecano.
However, in a match dominated by the European champions, it was the hosts who had the first clear opening as Alex Menendez shot just wide from Barca loanee Alen Halilovic's through ball.
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Luis Enrique also made five changes, but the star front three of Messi, Suarez and Neymar started after their incredible display in the 6-1 thrashing of Celta at the weekend.
Suarez had the first chance to extend his lead as the league's top scorer from Neymar's inch-perfect pass, but the Uruguayan fired straight at Ivan Cuellar.
Messi broke the deadlock with a deadly accurate drive into the bottom corner from 25 yards to become the first player ever to bring up a triple century of La Liga goals.
Yet, the lead only lasted two minutes as a brilliant counter-attack saw Pablo Perez pick out Menendez on the left and his low cross was swept home at the back post by Castro.
Barca promptly responded, though, as Suarez showed great strength to hold the ball up and then lay it off for Messi to fire into the roof of the net with the outside of his left foot.
Luis Enrique's men should have put the game out of sight before half-time as Cuellar flew to his right to prevent Messi from scoring a first-half hat-trick before Neymar curled the rebound against the post.
Barca's demolition of Celta in the final half an hour on Sunday was lit up by Messi's decision to pass a penalty into Suarez's path to complete his hat-trick.
And the former Liverpool striker may have regretted not returning the favour as Cuellar dived to his right to save Suarez's spot-kick after the 'keeper had brought down Neymar.
Barca have now missed eight of their 16 penalties this season.
However, Suarez made amends with a much harder opportunity 23 minutes from time when his left-footed effort curled in off the far post for his 40th goal of the season.
Arda Turan should have rounded off a 31st consecutive match without defeat for Barca with his first goal for the club, but he tried to square Messi's brilliant cross to Suarez and the ball flew inches wide.
Managing Messi a 'privilege' - Luis Enrique
Barcelona boss Luis Enrique described the fortune to have Lionel Messi on his side a 'privilege' after the five-time World Player of the Year scored his 300th La Liga goal.
Messi scored twice in a 3-1 win at Sporting Gijon on Wednesday to take his tally to 301 league goals in 335 games as Barca extended their lead at the top of the table to six points.
"To be able to count on Leo is always a privilege no matter how the opponent plays," said Luis Enrique.
The only negative for the European champions was another missed penalty, this time by Luis Suarez.
Messi had caused a worldwide sensation by passing a spot-kick into Suarez's path to complete his hat-trick in the 6-1 rout of Celta Vigo on Sunday.
However, between Messi, Suarez and Neymar, Barca have now missed seven of their 15 directly taken penalties this season.
It mattered little though, as Suarez made amends with a terrific finish for his 40th goal of the season 23 minutes from time.
"We want to improve in that aspect, but those that miss them are the ones that take the responsiblity to hit them.
"We have confidence in Leo, Luis and Ney. They are great penalty takers."
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