British-born Watson, 28, proposed to longtime girlfriend Azania Stewart after the starters were taken out of the game, held at Sports Authority Field in Denver. The Broncos beat the Packers 20-17.
"She said, 'Yes!' tweeted the Broncos, along with a photo that captured the moment. Watson is seen kneeling, while Stewart, is standing and covering her mouth in apparent shock. She is a member of the British national basketball team.
"Just spontaneous," Watson, who has known Stewart since they were 14, told The Associated Press. "It was her first NFL game. She's about to head overseas to start her season. She leaves tomorrow. It's something I've been thinking about for a while, been contemplating it, so what a perfect time to do it: in the stadium, our first game, in front of a beautiful crowd. I'm not really a public person, but I thought it would have been special."
And Watson's teammates apparently had no idea of his plans.
"That was very cool," Broncos quarterback Trevor Siemian said. "None of us had any idea, really. That was a surprise for sure. I can’t say I was expecting that or have seen that before. But I’m happy for them both, obviously."