Lamine Yamal linked up with Olmo to find a seam in the hosts' defence in the 62nd minute. Olmo took Yamal's threaded pass, shifted the ball to his left foot to open an angle around a defender, and fired the ball in off the underside of the bar.
While Olmo went on at halftime, Ferran Torres only played the final minutes and drilled in a second goal from angle in stoppage time.
Barcelona avenged a shock home loss to the Canary Islands club in November as they ensured they will spend another week atop the standings.
Hansi Flick's team are one point ahead of Atletico Madrid, who won 3-0 at Valencia earlier on Saturday. Real Madrid are three points back before facing Girona on Sunday without the suspended Jude Bellingham.
Barcelona play the first leg of their Copa del Rey semi-final against Atletico on Tuesday.
Julián Álvarez scored twice to lead Atletico to a comfortable win at Mestalla Stadium.
Antoine Griezmann played a part in both of Álvarez's first-half goals with a pair of finely-placed lobs inside Valencia's box.
Álvarez finished off a move in the 12th inside Valencia's area that started with a lifted pass from Griezmann that Samuel Lino volleyed off the bar.
Guiliano Simeone was first to the rebound and tapped it to Álvarez to ram into the net.
Griezmann was again left with space and time to think inside the area before he landed a perfectly-placed pass between Valencia's centre backs for Álvarez to gently nod off the turf and inside the post on the half-hour mark.
Ángel Correa completed the scoring with four minutes remaining.
"We are still in the fight," Álvarez said.
Valencia remained in the relegation zone.
Villarreal striker Ayoze Pérez netted his 11th league goal of the campaign in a 1-0 victory at 10-man Rayo Vallecano.
The result kept Villarreal in fifth place and challenging for one of the hampions League berths that go to the top four finishers. Athletic Bilbao are fourth and just one point ahead.
Rayo played with 10 men after Jorge de Frutos saw a red card for a studs-first foul just before halftime. The Madrid-based club also lost top midfielder Isi Palazón early in the game to an apparent leg injury.
Pérez scored in the 66th.
Espanyol claimed their first away win of the season thanks to a header by Fernando Calero and the goalkeeping of Joan García to beat Alaves 1-0.
The loss left Alaves coach Eduardo Coudet under added pressure with his team in danger of the drop.
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