The former couple was shoulder to shoulder this weekend -- the first time in a long time, especially amid all the nasty fighting that's been going on -- taking in their son Saint's soccer game in L.A. ... with mama bear, papa bear and his sister, North, watching from the sideline.

It's a somewhat startling sight, but a more than welcome one ... frankly, things have been nasty of late between these two -- so the fact they could come together like this is major.

As you can see, Ye was filming Saint play while Kim and North looked on attentively. At one point, Kanye crouched down and seemed pleased with what he was seeing on the field -- yep, he was in super dad mode here ... no doubt about it.

There was video taken of the scene as well, and although Kim and Kanye certainly shared the same space within short proximity to one another ... they don't appear to have interacted a whole lot, beyond herding the group in and out of the park, that is.

Still, as we said ... it's a huge step forward in their co-parenting relationship. Ye has been complaining a lot in recent weeks about custody issues -- alleging he hasn't been able to see all of the kids as much as he wants ... while Kim has claimed the exact opposite, saying he sees them whenever he wants. Now, it seems they're finally on the same page.

BTW, no sign of Pete Davidson anywhere here ... which is probably for the best. Something tells us KW still hasn't warmed up to him -- so no blending of families/partners just yet.