Giroud earned a brace for the Gunners, scoring a goal in each half that directly resulted from Southampton lapses in judgment.
The first came on an absolutely shocking decision from Southampton keeper Artur Boruc, who decided to get cute with a back pass instead of blasting it downfield. Giroud quickly turned into a ball-hawking defender, sticking to Boruc like glue before prying the ball free and tapping it into the net in the easiest finish you'll see.
Yes, Boruc arguably made the worst gaffe we've seen from a keeper in Premier League play this season, but give credit to Giroud for sensing an opportunity to strike and stealing a goal for the Gunners.
The second goal came after Jose Fonte was penalized for holding Per Mertesacker in the box during a corner kick late in the contest.
Giroud stepped up to take the penalty and calmly found the back of the net, giving Arsenal the insurance goal they craved (and deserved) after a swarming and positive effort in the second half, when they could have rested on their laurels and sunk back into a passive, defensive shell.
WhoScored.com named him Man of the Match and gave him an 8.4 match rating for his efforts, a justified score.
He now has seven goals and four assists for Arsenal in 12 games this season, and has put to rest the notion oft lamented by Arsenal fans this preseason that the Gunners were weak at forward. Yes, the team could use more depth at the position, but Giroud has certainly been up to the task thus far this year.
At his best, Giroud offers the size and play in the air of a traditional No. 9, but has the skill and vision to also facilitate the play for his teammates. His hold-up play has been strong this year, and though he can be maddeningly inconsistent at times, his style appears to perfectly accentuate Arsene Wenger's preferred tactics and philosophies.
Along with the unbelievable play of Aaron Ramsey—and the obvious impact of Mesut Ozil's addition—Giroud has been the most important Gunner this season. His impact was felt in the Southampton match, and if Arsenal is to remain atop the table, they'll need their in-form No. 9 to keep the good times rolling.