The Blues headed into Friday night's game in the Championship's bottom three but Che Adams's goal in the 19th minute was enough to claim a shock win over the division's first-placed side.
Prior to the international break, Birmingham lost 6-1 at Hull City, and Morrison claims that all the hard work put in by the players over the last fortnight has paid off.
"There's not a team anywhere that's worked harder in the last two weeks. It's paid dividends. You have to chase everything until the last minute," Morrison told Sky Sports News.
"Not only have we worked on fitness, we were organised. Everyone stuck with it, there were a few late bodies who came on and we looked good.
"We've got to get some momentum going, we've got a tough game next week and we've put a marker down with this result."