By the hour mark, the Argentine captain had made it 3-0.
Late goals from Gerard Pique and Luis Suarez completed the thrashing, with Dembele grabbing an assist, laying on the pass for the Uruguayan's goal.
After a slow opening, Barcelona took the lead after 26 minutes.
Suarez who shrugged off an injury whilst on worldwide break missed some decent chances, the closest being in the 55th minute when he blazed wide in the six yard box after a cutback from Messi.
'We are at the beginning of the season and the distances are not significant, but it is better to be ahead than behind.
However, the 22-year-old custodian could not repeat similar heroics during Barca's next effort on goal, which was fortunate to say the least, as Messi was on hand to simply tuck away his second of the evening following Jordi Alba's squared ball.
Far from fearing an imminent humiliation, Espanyol gamely responded and Barca goalkeeper Marc-Andre ter Stegen was grasping at air when Pablo Piatti's strike cannoned back off the post two minutes before half-time. "Game-by-game he keeps showing that Messi will be around for a long time to come".
Uruguay forward Suarez, who only returned from global duty on Friday, looked to be having one of those nights as he sent a cut-back from Messi over from six yards.
Five-time Ballon d'Or victor was in fine form, opening the scoring in the 26th minute, following up again ten minutes later, utilising expert service from Jordi Alba, sealing his hat-trick with more than 20 minutes remaining.
Espanyol were being outplayed but retained a sporadic threat, with Pique and Samuel Umtiti diverting Leo Batistao's 61st-minute shot behind.
The club promised two signings in the last week of the transfer window and none arrived and Bartomeu was booed by fans at Dembele's presentation in the Camp Nou stadium.
The French winger produced a quick show of footwork to turn Aaron Caricol, only to be brought down by the left-back, who was swiftly shown a yellow card.
Dembele has the unenviable task of replacing the departed Neymar and Barca's 105 million-euro man had to wait until 22 minutes from time for his debut as he replaced Gerard Deulofeu to a standing ovation.
Moreover, it was also found that 470 fake users and pages were connected to ads and operated in affiliation with one another. The drumbeat of news about Russia's role in the election has only helped push relations with the USA to post-Cold War lows.
Jaishankar said the two sides took a forward-looking and constructive approach during the meeting between the two leaders. Troops from both the countries had been stationed at the sector in Sikkim during the standoff, which had begun in June.
Rodman, who appeared on Trump's reality TV show " Celebrity Apprentice " twice, endorsed Trump for president back in 2015. However, Rodman's potential to broker peace depends a lot on what Trump thinks.
Still, that Ohio State front seven are outstanding, and the defense as a whole is better at creating turnovers. This season, the Buckeyes find themselves ranked number two in the country with a whole season ahead of them.
The depression is forecast to strengthen into a tropical storm within the next day or so, and it will receive the name Katia . So while Houston will be spared from another storm, eastern Mexico is at risk of localised flooding and potential mudslides.
He remembers past hurricanes and tropical storms, but never he says has he heard fear in his 80-year-old father's voice until now. But after the costly affects of Harvey, he's already working with Congress on additional funding for the island.
Dilshan Munaweera struck 53 and Ashan Priyanjan 40 not out in vain as the hosts finished a wretched run of clashes against India . Pandey finished off the game with a boundary that brought his maiden T20 fifty in 36 balls. "I want to play all the games".
Though CPI (M) had offered him a ticket to contest in the next assembly polls, he turned down the offer and later joined the BJP . Alphons added that though he had no great experience of the tourism sector, he would do his best to take it to new heights.
He added: "Physically I'm not in ideal condition, but when you play in the semi-finals of a Grand Slam , anything can happen. Del Potro, who beat Nadal in an epic Rio Olympic semifinal, knocked out Federer in the quarterfinals Wednesday.
They have conceded an average of 1.43 goals per league game in 2017, their highest rate in a calendar year since 1965. Still, AFC Bournemouth will be without a couple of players, most notably Stanislas, Francis, and Wilson.
The seventh season of Ryan Murphy's " American Horror Story " titled " Cult " will begin on President Donald J. As she sobs on her living room floor, the group talk about how they can't believe Trump has been elected.
USA calls for UNSC vote on North Korea sanctions
Meanwhile, the U.N.is considering fresh sanctions to counter North Korea's increasingly frequent and powerful missile launches. North Korea on September 3 detonated a hydrogen bomb that can be carried by an intercontinental ballistic missile (ICBM).
PM meets Aung San Suu Kyi
The Indian government is concerned about Rohingya immigrants in the country, and has been considering to deport them. The first such MoU between the two neighbours assumes significance for the northeastern region of the country.
Nissan Leaf arrives with 150-mile range and priced at $29990
Nissan said it would launch a longer, United States 200-mile rated version of the Leaf in 2019 that would be more expensive. Nissan has also introduced several new technologies on the second-gen Leaf, including autonomous driving functionality.
Android One: What It Is and All That You Need to Know
The chipset that ensures phones run longer and cool as a cucumber has been a runaway hit in the under Rs 20,000 price segment. The Xiaomi Mi A1 was unveiled in New Delhi , India earlier this week, boasting a lot of improvements in specs and design .
Bank of Canada surprises with interest rate hike
In its statement, the bank also said headline and core inflation have seen slight increases since July, largely as expected. At its previous meeting in July, the BoC raised its key rate for the first time in seven years, also by 25 basis points.