A late penalty from England Under-21 international Saido Berahino secured West Brom's first win under interim head coach Downing's stewardship, a result that ended a streak of nine Premier League games without a victory for the Midlands club.
West Brom are now four points clear of the relegation zone, and Downing was quick to express his satisfaction.
"It was a long time coming (the win)," Downing told BBC Sport. "I'm delighted for the club.
"Three games in eight days was a test. The momentum is changing for us - we've got three draws and a win in the last four games.
"There have been some good performances. We're building slowly and this will be a massive boost for everybody."
Downing reserved praise for Berahino and refused to rule out a call-up to the England senior side for the 20-year-old.
"He's a goalscorer and I had no doubts about it when he stepped up," Downing added. "It was an important penalty and I think he knew that.
"He's a good player, he's still got a lot to learn. He's a natural goalscorer, he has this ability to score important goals.
"He'll certainly be considered (for England) if he continues scoring goals."
