Yeah it was really nice to watch us defend so valiantly. The arrangement on the left side is to cater for Auba's attacking need.
When eereyout of position, we operate a back five, with Ainsley dropping deep to join the defenders, while in attack, we basically have two wing backs, but Tierney more central and Ainsley operating on the flank. If you watch Auba's goal against Liverpool and the one he scored yesterday, you'll find that they were identical. Both goals had Tierney and Ainsley overlapping.
It is an interesting tactics that gives us more protection at the back and doesn't reduce our attack
this is literally the same :D