How to reduce carelessness?

3 out 8 games I played today (I'm Porto) was in the lead 2-0, 2-0 and 3-0 and in all of them conceded 2 or 3 goals but won all 3 of the games thanks to injury time winners. But it annoys me when were dominating and then concede 2 or 3 goals in 10min against weak teams.

So how can I reduce this and complacency against weaker teams?

Increase timewasting, keep passing simple, attack less, maybe bring on extra defensive players, reduce creative freedom, change closing down and tackling settings..

Yet so often none of the above works...

It should do the majority of the time. If not, your players may be to blame. Low concentration, tiredness etc.

Yet so often none of the above works...

I agree

Drop down to counter/defend options when you go 2-0 up, and retain posession / pass to feet shouts.

Works 95% of the time for me.

But don't Defend Deep and then Hassle Players at the same time, because you will be dragging your players way out of position by doing this.

If you're 3-0 up @ half time and complaining about losing, I take it you're not stoke city. You're probably the better team, if you're playing at home, and comfortable favourites, I usually start with attacking. Going to control can do the trick for 2nd half. I've noticed AI changes tactics VERY often @ half time. Make sure you counter this right away. If you play defensive/counter, you're letting your opponent control the game, which doesn't make too much sense to me unless they're better. Check out any top 4 vs avg match irl in the prem, the top 4 team will never go for a 40-60 possesion approach in the 2nd half. Instead, they just slow down a bit (control) and make sure they're not gonna be too vulnerable for the counter (again, control). I say, try control.