I don't think this game is going to be that easy for arsenal just like the way you are putting it and remember Southampton have a of playing with these big teams and I can remember well that the premier league at this stage of the season, the smaller team like Southampton are the more deadly ones because they are fighting the battle of relegation and can take any big team by surprise and defeat them so I would advice for arteta to be very cautious of this nights game because any slip up the league will surely be Manchester city own and all their hard work this season would end up a second place reward.
Southamton had a difficult mission against Arsenal today but I'm sure they won't succeed. Southampton desperately wanted to get out of the relegation zone which was increasingly becoming a reality for them towards the end of the season but with Arsenal I think their mission is failed. It's too hard to expect Arsenal to lose to Southampton, even I don't believe Southamton can draw at the Emirates. Arsenal are struggling to have a safe distance from the pursuit of Manchester City, so their victory is expected.
Of course there is a lot of pressure on Arsenal since they failed to win two match in a row, but in this match I think the probability of winning is very favorable. Arsenal will likely appear to dominate over Southampton, so they will win it.