City went ahead in the early stages when Yaya Toure converted a penalty following a foul from Jose Fonte on Edin Dzeko, only for Southampton to equalise when a foul from Pablo Zabaleta on Jack Cork allowed Rickie Lambert to score from the spot.
Southampton lost Jay Rodriguez to a serious-looking injury in between those goals and after they'd impressed they ended up 3-1 down at half-time following two goals in first half stoppage time.
The first of those was hugely controversial, as David Silva looked to be in a clear offside position before setting up Samir Nasri, before Edin Dzeko headed in a third.
Substitute Stevan Jovetic tapped in a fourth goal in a more subdued second half.
Here are six lessons learned from Saturday afternoon: