Walcott's goal came late in the game after Arsenal had soaked up everything L'OM had to offer. Kieran Gibbs, who was superb all night at left-back, crossed for the England flyer to smash the ball home after Jeremy Morel's attempted clearance.
The second goal came from the boot of Ramsey, who added his seventh goal of the season. The Welshman has been brilliant this term and is the real inspiration behind Arsenal's early good form.
He took his lucky No. 7 with devastating ease. Having controlled the ball, he evaded two tackles before firing in from the edge of the box. It was a great goal despite the slight deflection.
In truth, the game was best described as a tactical affair. Marseille created the better opportunities in a tight game. Mathieu Valbuena impressed from center midfield for the French team, but they lacked a cutting edge up front, where Arsenal dealt with them easily.
Marseille did manage to score a late consolation goal after Ramsey took Andre Ayew down after his own poor control in the penalty area. Ayew then dusted himself off and stepped up to score, but it was a case of too little, too late.
It was almost, in many ways, the perfect away performance by Arsene Wenger and his team.
Here, Bleacher Report offers five things we learned from Marseille vs. Arsenal...
Theo Walcott is one of the most honest players in the Premier League.
The 36-times-capped England international seems to have been around for years at this stage of his career. He has played over 180 matches for Arsenal and almost 300 games in his career's entirety.
With that in mind, it is worth remembering that Walcott is just 24.
As an instinctive player, Walcott is always going to garner attention. He is the kind of player fans and the media love to see, and he is very exciting. That attention also has its downside—he is also more likely to be criticized for his mistakes than others.
Last weekend, Arsenal's win was all about Mesut Ozil and Aaron Ramsey. They, quite rightly, took all the headlines as Walcott copped most of the flak for a series of misses.
If he was a man with less character, he would have let that criticism get to him and played poorly against Marseille. In similar situations, certain players go back into their shells and try not to make mistakes.
That simply does not faze Walcott because he is an honest player. He is not afraid to do the right thing on the pitch, and if it means having to suffer the slings and arrows that follow, he will endure.
That outlook and honesty got him into the position to score from Kieran Gibbs' cross.
There is little doubt that Walcott is far from the finished package—he may never be. However, he never gives less than 110 percent and players like that can be worth their weight in gold.
Over the last couple of seasons, the strength of Arsenal's squad depth has been questioned.
Sure, the Gunners may be lacking world-class talent in a few positions, especially when you compare them to previous great teams. However, Arsene Wenger's club now have Premier League talent in pretty much every position. They won't win the Premier League or the Champions League without changes, but they seem to be going in the right direction.
The starting lineup for the Champions League game against Marseille looked like this;
Arsenal: Szczesny, Sagna, Mertesacker, Koscielny, Gibbs, Flamini, Ramsey, Walcott, Wilshere, Ozil, Giroud. Subs: Fabianski, Vermaelen, Monreal, Jenkinson, Miyaichi, Akpom, Hayden.
Now look at the injury list:
Santiago Cazorla, Tomas Rosicky, Abou Diaby, Mikel Arteta, Alex Oxlade-Chamberlain, Lukas Podolski and Yaya Sanogo.
Also, consider that Per Mertesacker only made the team at the 11th hour after missing the victory over Sunderland at the weekend. Olivier Giroud also passed a late fitness test to play after picking up a knock in the same match.
If Wenger can add a few key players in certain positions like center-back and center-forward, the Gunners could end up having one of the strongest squads in Europe.
Arsenal only made one change from the team that beat Sunderland at the weekend, and that was at the back. Mertesacker came in for Carl Jenkinson as Bacary Sagna reverted to his normal position at right-back.
Up front, the Gunners put out the exact same side.
However, comparing Marseille to Sunderland is like comparing apples and oranges.
Against the Black Cats, the Gunners ran amok and destroyed Paolo Di Canio's team with relative ease. Their midfield was fluid. Any time Sunderland broke through, they were easily dealt with.
Marseille were a completely different proposition.
Mathieu Flamini's lack of mobility and ball-playing skills in midfield were highlighted as Mathieu Valbuena enjoyed the upper hand. Further forward, Jack Wilshere kept coming inside from the left and crowding Mesut Ozil as Theo Walcott hugged the right side of the pitch.
Flamini's and Wilshere's poor games combined to give Marseille free reign on their right-hand side and through the middle. Olivier Giroud was isolated, and Walcott and Ozil barely got a touch in the first half. Aaron Ramsey, Arsenal's star of the early part of the season, was anonymous.
They all improved in the second period, especially Ramsey, but the problems on the left remained.
Wilshere is the best center midfielder the Gunners have and should be playing there ahead of Flamini, despite the Frenchman's more robust style. That kind of style matters less in the Champions League than it does in the Premier League. Without Wilshere in the center, they were badly wanting.
Being an avid observer of Champions League football since it began in 1992, I can honestly say that I have never seen a grouping as tough as the Gunners' group this term.
Borussia Dortmund, last season's losing finalists, led by the supreme Jurgen Klopp, are one of the best footballing sides in the world. Dortmund currently sit on top of the Bundesliga with 15 points from their first five games and have scored a whopping 15 goals.
Napoli, who played Dortmund as Marseille entertained the Gunners, have also started off well to life under Rafael Benitez. The ex-Liverpool, Real Madrid and Chelsea boss took over last summer and immediately set about changing their setup from a 3-4-3 formation to a 4-2-3-1.
They have bought and sold intelligently and are also top of their league, Serie A, albeit after just three games. James Horncastle's recent excellent piece for Who Scored pointed out how the under-the-radar signing of Jose Maria Callejon has made a huge difference in Naples. He could be a real star someday.
Arsenal need no introduction to their fans. They sat atop of the Premier League for a few hours until Liverpool scraped home to a 2-2 draw to Swansea City to reclaim the top spot. Arsene Wenger's team famously lost against Aston Villa on the opening day of the season. However, they have been excellent since then.
Marseille have only lost once this season too, and that was to high-spending Monaco. In a league where Paris Saint-Germain FC and Monaco can outspend their rivals by unbelievable amounts, Marseille are never going to win the league. The best they can offer is intelligent signings and intelligent football. One thing that can be said about Elie Baup is that his teams are always well-constructed and intelligent.
Kieran Gibbs had a stonking game against Marseille.
There was a massive imbalance in midfield ahead of him. The likeable 23-year-old was forced to deal with Dimitri Payet and Rod Fanni throughout the game. He was more than excellent in his positional play both on and off the ball.
Like all good defenders, he concentrated upon his main aim, to defend his goal with his life. As the game wore on and the opportunities began to arise, he broke forward with aplomb.
He picked up Ramsey's pass to the left and produced a superb cross for Theo Walcott to power home.
This season will be his sixth year as a first-team squad player at Arsenal. He has only played 112 games due to a number of injury problems. If he can put these behind him, he will claim the England No. 3 berth from Ashley Cole.
On current form, it is only a matter of time.