An injury-time goal by substitute Aaron Ramsey gave Arsenal a 1-0 win at Marseille on Wednesday that enabled Arsene Wenger's side to leapfrog their opponents to top spot in Champions League Group F.
The Welsh midfielder applied a cool finish in the dying seconds of a forgettable game that had betrayed the fragility and lack of confidence that have plagued both sides' starts to the season.
Marseille had not conceded a goal in the competition prior to Ramsey's intervention, but they now find themselves a point behind Arsenal prior to the return fixture at the Emirates on November 1.
"We left it very late," admitted Arsenal coach Wenger.
"I think overall we had a difficult start. We lost balls in the first half, which was down to the fact Marseille pressed us well.
"In the second half we took over. I don't think Marseille were ever dangerous in the second half.
"They defended well but in the last 15 minutes we created chances and in the end we were rewarded for the fact we kept going and got a very important victory.
"There was a bit of luck, of course, but the three points are very welcome, even though it was very difficult to swallow for Marseille."
The chances of seeing both sides in the last 16 were enhanced by Borussia Dortmund's unexpected 3-1 defeat at Olympiakos, however, which leaves the German champions bottom at the group's halfway point.
Renovation work has reduced Stade Velodrome's capacity to 42,000 but Marseille's early-season struggles meant there were only around 30,000 fans present to see a match in which a sense of occasion was conspicuously lacking.
Marseille sported their orange third kit, with Arsenal in uncharacteristic blue, and referee Damir Skomina added a liberal splash of yellow with early bookings for Arsenal pair Alex Song and Andre Santos and OM's Andre Ayew.
Ayew's name was taken for protesting over Skomina's failure to award a penalty for a handball by Carl Jenkinson, and television replays suggested the hosts could count themselves unfortunate.
Marseille had started strongly but their goal was the first to be threatened, with Souleymane Diawara obliged to clear a looping header from Robin van Persie off the line.
For all their endeavour, OM were toiling in attack, but Loic Remy provided a flash of brilliance on the half hour, jinking inside Per Mertesacker and Jenkinson from the byline before his shot was blocked by the latter.
Moments later it was Lucho Gonzalez's turn to draw gasps from the Arsenal fans, as he stole in front of Mertesacker to toe Mathieu Valbuena's cross across goal and wide.
Lucho and Ayew sparked an unseemly scramble in the Arsenal box minutes shy of the hour, before a defensive error by Nicolas N'Koulou almost gifted the visitors the opening goal at the other end.
The Cameroon centre-back allowed the ball to run beneath his foot, giving Walcott a clear sight of goal, albeit from a narrow angle, but OM captain Mandanda saved with his feet.
Mandanda then denied van Persie, but Marseille looked to be safe until Ramsey was gifted acres of space on the left-hand side of the OM area and calmly placed the winner inside Mandanda's right-hand post.