Arsenal recovered from an unimpressive first half to defeat Olympique Marseille 2-1 on Wednesday in a clinical opening to their Champion League campaign.
Theo Walcott volleyed home in the 65th minute after benefiting from Jeremy Morel's defensive blunder before Aaron Ramsey put the result beyond doubt seven minutes from time with a deflected low shot.
Arsene Wenger's side, who looked listless in the first half, are level in Group F with Napoli, who beat last season's runners-up Borussia Dortmund 2-1.
Olympique Marseille had a handful of chances with Andre-Pierre Gignac, Andre Ayew and Rod Fanni coming close to scoring before Jordan Ayew reduced the arrears with a penalty in added time.
Wenger made just one change for the match, with centre-back Mertesacker brought in to play alongside Laurent Koscielny.
The pair lined up together last time Arsenal visited the Marseille in October 2011, keeping the hosts at bay as Ramsey came off the bench to snatch a 1-0 win.
Much has changed since at the Stade Velodrome since then, most obviously the structure itself.
Gone is the Tribune Jean-Bouin, replaced by cranes and a concrete shell as the stadium is redeveloped ahead of hosting Euro 2016.
It means the venue is as much a building site as a football stadium, but the home fans made it as intimidating as ever.
The teams were welcomed onto the pitch by a wall of sound, with Marseille first to threaten.
Gignac's flick goal wards had supporters on their feet, with Wojciech Szczesny then having to deal with a long-range Mathieu Valbuena effort.
The frenetic start continued as Arsenal went up the other end in search of an early goal.
A Mesut Ozil cross was nodded goalwards by Walcott, only for Nicolas N'Koulou to clear from danger.
The forward was proving a pest in the early stages, forcing Steve Mandanda into action before landing a chip on the roof of the net, albeit from an offside position.
The tempo soon calmed, though, with both sides content to keep possession as they searched for an opener.
Valbuena tried and failed after being set-up by Andre Ayew in the 19th minute, before the roles reversed two minutes later.
The diminutive playmaker whipped in a corner and the Ghana international found space to flash a header just wide.
It was the closest either side had come to an opener, although the north Londoners may feel aggrieved not to have been awarded a penalty soon after.
Ozil swung in a corner from which Mertesacker was booted in the face by Alaixys Romao, but referee Olegario Benquerenca showed no interest in awarding a penalty.
Only last-ditch defending by Mertesacker prevented a Dimitri Payet ball across the six-yard box being directed home as Marseille ended the half on top, with Gignac seeing a glancing header fly just over.
Marseille continued in the ascendancy after the restart, with Fanni smashing a half volley inches wide.
Mandanda was forced into a fine reaction save to deny Gibbs finishing a move he started, before the Marseille goalkeeper denied Jack Wilshere.
It was not all Arsenal, though. Szczesny thwarted a driven Payet effort and Gibbs came to Mertesacker's rescue in the 60th minute just as Gignac was about to nod into an open goal.
It was a missed chance Marseille were made to pay for just four minutes later.
Morel misread a Gibbs cross and the ball fell kindly for Walcott, who lashed home impressively from close range.
Payet and Valbuena kept threatening as Marseille pushed for an equaliser, but Arsenal were still proving a threat - highlighted by a Giroud header just wide.
Ozil also came close in the closing stages, before Ramsey put the match out of sight by shrugging off Marseille defenders to fire home.
Jordan Ayew struck home a stoppage time penalty after Ramsey was adjudged to have tripped Andre Ayew, but it was a mere consolation.