Zendaya and Tom Holland made it abundantly clear Thursday night they're all-in on Steph Curry and all-out on LeBron James -- cheering their faces off for the Warriors against the Lakers!!

The A-list actors hit up Game 2 of the Golden State vs. L.A. playoff series at Chase Center in San Francisco ... and while they somehow didn't have the best seats in the building, there was no question whatsoever to whose back the couple had.

Zendaya, wearing a black Golden State cap for most of the game, roared every time the Dubs made a big basket. And, like a great boyfriend, Holland was right there joining her for the celebrations throughout the night.

Of course, the fandom shouldn't surprise many -- Zendaya is an Oakland native.

Seems all the cheering worked well for the home team ... 'cause Curry and the Warriors went on to blowout the Lakers, 127-100 -- evening up the playoff series at 1-1.

The duo, though, wasn't the only celebs in the arena rooting on Curry at the big game ... 49ers legend Joe Montana and current Niners stars Christian McCaffrey, George Kittle and Sam Darnold were also there.

In fact, at one point, McCaffrey, Kittle and Darnold seemed to have some fun with Holland by pretending to shoot Spider-Man webs out of their hands while sitting courtside.