I can't see Manu starting because of the reasons people have indicated in the posts here: 1) the second unit needs his leadership (Diaw can create plays but lacks the leadership that Manu brings), and 2) Manu can't match Green's defensive abilities.
In terms of Mills starting, I think it would be worse. Presumably the point would be to use him to spread the floor. Problem with that is that, similar to Manu, Patty would be a defensive liability compared to Green, and his strength is in 'letting it fly", but the first string is a bit too orchestrated for that.
If there is to be a change in the starting backcourt (and I'm not in favor of it at this point), I would think you would have to replace Parker with Manu. Then put Parker in with the second unit along with Green and Diaw. Problem then is that you use too many Manu minutes, and we all know what happens when Manu gets used more minutes than his aging body accommodates.
The only real problems I see with the starting unit is that the team is not accustomed to Kawhi and LA being the first and second scoring options. They are all trying very hard to make that happen, but it takes Green out of his rhythm (as someone else pointed out), and we very often end up with crowded spacing when Duncan and Aldridge are near the paint and Kawhi is trying to iso with his back to the paint. It is just too crowded. As Kawhi improves at passing out of double teams to the right shooter (he is learning this skill but it is taking a bit), and as Aldridge gets more comfortable with where he needs to be in general, and as Kawhi and Aldridge become more comfortable in an offensive set that involves either or both of them going one-on-one, I think things will improve.
Remember last year when the beginning of the season was a mess of watching four of our starters watch Kawhi try to iso while standing and waiting to see if it would work? It was not pretty.
This year is not pretty.
I think the call for a line-up change in the backcourt is premature, but I don't expect it to get very pretty any time soon.
The bajillion turnovers last night was a combined function of Washington turning up the speed and us being too dumb not to fall for it, and the (too) frequent unforced errors by not being sufficiently focused.
We'll get there I think...
give 'em time.