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. However, Barca were in irresistible form as they swept them away in the first half to consign Periquitos to a fourth straight league defeat.
Messi completed the rout with another special free kick in the 65th minute and VAR ruled out a consolation from Oscar Duarte for offside at the other end. This made it 3-0 before half-time and was an accurate representation of how well Barcelona were playing, although Espanyol weren't playing bad by any means.
Messi celebrated with Dembele when the Frenchman scored his goal, and the No.10 is convinced the youngster has what it takes to succeed at Barcelona.
The Argentine bagged two impressive free-kicks as the LaLiga champions thumped Espanyol on Saturday evening.
Lionel Messi celebrates against Espanyol (Joan Monfort/AP).
Barcelona were caught out at the back in the 74th minute when Duarte stabbed the ball in at close range from a free-kick.
Suarez was able to get on the scoresheet, though, when Dembele found him with a defence-splitting pass and he was able to hold off the defender before shooting through Lopez's legs from a tight angle.
Espanyol started the second period on the front foot, but aside from a Sergi Darder attempt which missed the crossbar, the home supporters did not have too much to shout about.
'Messi is just extraordinary.
"It's very worthwhile to win at Espanyol this season", he continued.
"They've not been fair with Messi".
Baptistao then headed into the arms of Ter Stegen in the final moments as the match ended 4-0, with Barcelona far too strong for their rivals on the night.