Messi scored two stunning free kicks to make it 23 derby goals, while fellow forwards Dembele and Luis Suarez also registered at the RCDE Stadium. A goal in each half with an assist in between saw the 5th best player in the world, according to France Football, break another La Liga record.
The win sees Barcelona go three points clear at the top of the LaLiga table, whilst Espanyoldrop to ninth.
The Barcelona captain, who finished only fifth in this year's Ballon d'Or vote, curled in another superb dead-ball strike on 65 minutes to cap a fine individual and team performance.
Chris Hughton Had Little Sympathy For Shane Duffy
They had already been one up through a Glenn Murray penalty just minutes before Duffy's moment of madness. Brighton are 10th in the table with 21 points while Burnley are second from bottom on nine points.
Substitute Philippe Coutinho was denied the icing on top of the cake by Lopez's strong left hand shortly after coming on, before one incident pretty much summed up Espanyol's night.
Barcelona were caught out at the back in the 74th minute when Duarte stabbed the ball in at close range from a free-kick.
Dembele turned provider this time, slipping his fellow forward in in the left-hand channel, with Suarez doing brilliantly to hold off the challenge of a defender and somehow squeeze a finish through the legs of Lopez and into the far corner from the narrowest of angles.
Espanyol went looking for a lifeline at the start of the second half, but Barcelona remained unsafe on the break.
Espanyol looked for a way back in to the match as Duarte's downward header at the far post was blocked by Marc-Andre ter Stegen.
Victor Sanchez headed over the Barcelona crossbar 10 minutes from time as Espanyol continued to search for a goal, and it nearly arrived when Baptistao struck towards the far corner, but the ball just deflected wide.
Barca's front three were all in fine form but Messi was the conductor at the heart of all their play.
Chinese probe heads for far side of the moon
Chang'e 4 is the next in the line of China's Chang'e missions, and would be the first craft to land on the Moon's far side. Beijing is planning to send another lunar lander, Chang´e-5, next year to collect samples and bring them back to earth.
Five-star recruit Vernon Carey commits to Duke
Michigan State , which went down to the wire with Duke for Carey, is the perceived favorite in the 247Sports Crystal Ball. Carey joins fellow five-star recruit Wendell Moore and four-star Boogie Ellis as members of Duke's 2019 recruiting class.
Bill Cosby Blamed For "Baby It's Cold Outside" Radio Ban
Since then, Canadian broadcasters Bell Media, CBC Radio and Rogers Media have also made a decision to drop the song this year. Loesser said she was upset about the furore because "it's a song my father wrote for him and my mother to sing at parties".
Derek Fisher joining LA Sparks as head coach
According to ESPN basketball insider Adrian Wojnarowski , Fisher has been hired as head coach of the WNBA's Los Angeles Sparks . He went 17-65 in his first year as head coach of the Knicks and was sacked the following season after the team's 23-31 record.