Dembele produced his best performance since his £135.5million move from Borussia Dortmund last summer with his pace and footwork proving impossible to contain.
“Dembele had a great game. He’s a very talented player indeed. His last goal was lovely,” Valverde said in quotes reported on the Barcelona website.
“We are expecting big things from him. He’s still very young and has a long time ahead to show his class. All new players need some time to adapt.
“We totally dominated the play in the first half and created loads of chances to score.”
Andres Iniesta, who is playing his final season in Spain, set up two goals to help Barcelona continue their quest to become the first team to finish a LaLiga season unbeaten.
“We’re very pleased with the match. We still have the goal of completing the season unbeaten. That would be very special,” Iniesta said.
“In sport you are looking for motivations. We don’t want to drop our guard because we have a very nice target, to be unbeaten.”
Sevilla remain in the hunt for a Europa League spot as Joaquin Caparros secured his first win since taking temporary charge with a 3-2 win over Real Madrid at the Ramon Sanchez-Pizjuan.
The visitors, who could have moved above city rivals Atletico and into second with a win, were without the injured Cristiano Ronaldo and suspended Gareth Bale and it showed as they posed little attacking threat.
Wissam Ben Yedder and Miguel Layun gave Sevilla a comfortable half-time lead, and after Sergio Ramos missed a penalty for Real, the defender then deflected the ball past his own goalkeeper to make the points safe.
Borja Mayoral’s 87th-minute header and a successful Ramos penalty in stoppage time gave the scoreline a flattering look as impressive Sevilla moved seventh, three points behind Villarreal but with an inferior goal difference.
After a quiet opening 10 minutes, Franco Vazquez had the first chance of the evening for the home side but his shot cleared the crossbar.
The same player saw a shot blocked by Ramos, before Sevilla’s early dominance paid off in the 26th minute.
Nicolas Pareja played a long ball towards Luis Muriel and his flicked header fell for Ben Yedder to slide the ball under goalkeeper Kiko Casilla.
Nacho almost turned the ball into his own net as he looked to clear another opening, but it was not long before Sevilla did add a second.
A superb counter-attack saw Steven N’Zonzi set up Layun and he lashed the ball home on the stroke of half-time.
Real Madrid were handed a lifeline early in the second half when Lucas Vazquez was brought down in the penalty area. Ramos stepped up and cracked his spot-kick against the crossbar.
Muriel almost added a third when through one-on-one and Sandro Ramirez glanced a header inches wide.
Sevilla looked to have sealed the points when Gabriel Mercado’s speculative effort took a huge deflection off Ramos and gave Casilla no chance.
Mayoral’s header was followed by another Ramos penalty, but there was no more time for Real to snatch an unlikely, and perhaps undeserved, equaliser.
Ousmane Dembele scored twice as Barcelona thrashed Villarreal 5-1 on Wednesday and edged closer to their first ever unbeaten season in La Liga.
Lionel Messi volleyed in a sumptuous pass from Andres Iniesta at Camp Nou to put Barca three up at half-time after Philippe Coutinho and Paulinho had scored one apiece in the first 16 minutes.
The second period, however, belonged to Dembele, who capped an excellent individual display with two goals after the Frenchman’s sensational run had also earlier set up Coutinho.
Villarreal managed a consolation when Pablo Fornals’ shot deflected in off Nicola Sansone but any fears Ernesto Valverde’s side would feel the effects of Sunday’s ‘Clasico’ proved unfounded.
The league leaders moved 15 points clear of Atletico Madrid at the top while Villarreal stay sixth.
Barca drew last weekend against Real Madrid, despite playing the entire second half with 10 men, and they now need only avoid defeat in matches away at Levante and home to Real Sociedad to complete the campaign as invincibles.
It would be the first time a team has finished a 38-game La Liga season unbeaten and the first in any format since Real avoided defeat in a division of only 10 teams in 1932.
Already crowned champions and winners of the Copa del Rey, Barca were controversially denied a guard of honour by Real but Villarreal were happy to perform the ‘pasillo’ as the hosts walked out before kick-off.
Valverde left some key players out, with Marc-Andre ter Stegen, Luis Suarez, Jordi Alba and Ivan Rakitic all missing from the starting line-up.
Messi, however, was included despite calls for the Argentinian now to be rested ahead of this summer’s World Cup.
It meant a start for Dembele, who took his chance to impress with the stand-out performance of the night.
Dembele has endured a difficult debut season since joining for 147 million euros from Borussia Dortmund last year but Barcelona president Josep Maria Bartomeu has said this week he is not for sale, and the 20-year-old delivered the perfect response.
His run that set up Coutinho’s opener in the 11th minute was arguably the moment of the match as he picked up the ball 10 yards inside Villarreal’s half before driving past three defenders and unleashing a shot.
Villarreal goalkeeper Sergio Asenjo palmed the ball away but only to Coutinho, who was left with a tap-in.
Paulinho doubled Barca’s lead five minutes later after a brilliant Iniesta pass allowed Lucas Digne to slide the ball across goal. Paulinho finished at the back post.
Iniesta was at the heart of the home side’s third too, this time a chipped ball playing in the darting Messi, who side-footed home on the volley.
Villarreal pulled one back after half-time when Fornals’ shot clipped the shoulder of Sansone to wrong-foot Jasper Cillessen.
But Dembele grabbed a late brace, his first an easy finish after a brilliant run by Rakitic down the right, his second coming after he sped away from Villarreal’s defence, and lifted the ball over the helpess Asenjo.