Barcelona gets revenge for their Copa del Rey to defeat here two-and-a-half weeks ago as Dembele slotted home from a Messi through-ball before the provider turned scorer with an individual goal in the 85th minute to put the game to bed.
The result sees Barcelona leapfrog Real Madrid into second in the table, but Los Blancos have a game in hand on them.
Barcelona and Sevilla will face again on Wednesday as the former host the latter in the second leg of the Copa del Rey semi-final, with Barcelona needing to overturn a 2-0 first-leg deficit.
Barcelona started well and was the first to go close when Frenkie de Jong raced away on 20 minutes and released Dembele whose cross-shot was saved by Bono.
Messi then tried to catch out Bono at his near post with a shot from a free-kick that everyone expected him to cross.
Ivan Rakitic reacted badly to a late challenge from Oscar Mingueza. Sergio Busquets had to intercede as the former Barcelona midfielder faced Barça’s young defender. Barcelona had the upper hand and the goal was not long in coming.
Messi found himself in space on the halfway line for 29 minutes and he lifted his head and sighted Dembele who was ready to sprint ahead.
Barcelona had enjoyed a good first half but they could have lost Messi to a red card before the break. He was harshly booked for a foul on Fernando. Replays showed he made no contact with his opposition but that the Brazilian caught him on the back of the calf.
But then, having been yellow carded, he put an arm on Kounde as the French defender got away from him and Sevilla players urged the referee to show the second caution.
The Sevilla bench protested so much that coach Julen Lopetegui was shown the yellow card.
The Sevilla coach wasn’t just upset with the decision; he was unhappy with his team’s performance and there were three changes at the break with Karim Rekik replacing Diego Carlos, Suso replacing Papu Gomez, and Youssef En-Nesyri replacing Munir El Haddadi.
The last ten minutes were frantic as En-Nesyri scored and had the goal ruled out because he handled it as he turned. He then went down for a penalty but was told not to dive.
Barcelona lost Araujo to injury and he kicked over a row of seats as he walked off the pitch frustrated twisting the same ankle that had kept him out for three weeks.
Barcelona made the most of the interruption in play to further break Sevilla’s rhythm and Dembele was booked for leaving the pitch too slowly when replaced by Martin Braithwaite.
Koeman’s team looked to be hanging on but there was to be no nervous period of injury time as Messi got the second after a neat assist from Ilaix.