Russell Westbrook had touched down in Denver -- getting ready to take on the Nuggets -- when all of the sudden ... BOOM, IT'S MICHELLE OBAMA!!!
The Oklahoma City Thunder star has a game tonight at the Pepsi Center -- the same spot where Michelle O had a big event Thursday to promote her book, "Becoming."
Unclear who spotted who ... but Russ was definitely excited to see the former First Lady and posted the pic on Instagram.
"It was insane running into Michelle Obama. She has been such an inspiration to my family, and I can't wait to read her new book Becoming," Westbrook wrote.