The result has moved Barcelona 12 points clear at the top of the table, while Espanyol stay down in 15th spot following the rain-soaked derby.
As for Espanyol, an attacking side saw Leo Baptistao and Moreno both start in the final third of the field.
Luis Suarez had a couple of half-chances in the opening 10 minutes of action, but neither effort threatened to find the back of the net as Espanyol held firm in the early exchanges of the clash.
Coutinho came close to a spectacular first Barcelona goal when he unleashed one from the edge of the box in the 22nd minute, but the Brazilian international saw his effort strike the crossbar.
Espanyol's first opening arrived in the 26th minute when Baptistao drove to the edge of the Barcelona box before striking towards goal, but Marc-Andre ter Stegen made the save.
Baptistao had another opportunity in the 33rd minute when he rose highest inside the Barcelona box, but the Brazilian's bullet header missed the crossbar as the score remained goalless approaching the latter stages of the first period.
It was Barcelona that were pressing for the opener in the latter stages of the first half, although neither Luis Suarez nor Paulinho managed to test Espanyol goalkeeper Diego Lopez with efforts in the final exchanges.
Espanyol actually had the ball in the back of the Barcelona net early in the second period, but Moreno's goal was disallowed after Baptistao was adjudged to have run it out of play before delivering into the box.
Messi and Sergi Roberto both came off the Barcelona bench just before the hour as the rain continued to fall, which made certain areas of the field almost unplayable.
It was Espanyol that made the breakthrough in the 66th minute when Moreno headed a wonderful Sergio Garcia cross into the back of the net from close range.
Jordi Alba followed Roberto and Messi off the Barcelona bench as the away side looked to level in the latter stages, but chances were few and far between due to the state of the pitch.
Barcelona did level in the 83rd minute, however, when Pique rose high to head a Messi cross into the bottom corner.
Both teams had half-chances in the latter stages, although neither really threatened to win it as the points were shared in Catalonia.
ESPANYOL (4-4-2): Diego Lopez; Navarro (Javi Lopez 76'), David Lopez, Naldo, Aaron; Sanchez, Granero, Darder, Jurado (Garcia 61'); Baptistao (C.Sanchez 86'), Moreno
BARCELONA (4-3-3): Ter Stegen; Semedo (Roberto 59'), Pique, Umtiti, Digne (Alba 75'); Busquets, Iniesta, Paulinho; Coutinho, Suarez, Alcacer (Messi 59')