Russell Wilson is already building up serious chemistry with his new star receiver Courtland Sutton -- hitting the dude in stride for a huge TD pass in a workout in the quarterback's backyard on Tuesday.

The new Denver signal-caller just posted the vid -- his first-ever in Broncos gear -- and even though he's on a new squad, his arm certainly still looks the same.

Watch the clip, Wilson fired off a 50-yard strike to Sutton, who came down with the ball while sliding into the endzone.

The two dapped up on the field after the play -- and following the training session, Russ was clearly hyped about his new teammate.

"Uh oh," Wilson wrote, adding a "😏" emoji.

Of course, the sight is going to make Seahawks fans cringe -- particularly after Seattle brass said in statements last week that it was Wilson who originally asked for a trade.