Birmingham head coach Lee Bowyer was delighted to start the new season with a 1-0 win at Sheffield United, following Maxime Colin's first-half goal.
United went close to making an almost immediate response when Oliver Burke's low, angled shot struck the near post.
Oliver Norwood then saw an opportunity to try his luck from distance and his shot went narrowly wide of Matija Sarkic's right-hand post.
Lukas Jutkiewicz wasted a great chance to put Birmingham further ahead, putting his header wide of the target.
Scott Hogan then spurned an even better opening, lifting the ball over the bar from inside the six-yard box after getting on the end of a Jutkiewicz knock-down.
McGoldrick curled a shot just wide before Colin's header was ruled out after a push by Jutkiewicz on Osborn.
Blades players appealed for a penalty when Fleck's drive struck the arm of Gary Gardner, sending the ball wide, but they were only awarded a corner.
With Birmingham defending in numbers, United never seriously threatened to level in the closing stages, going down to a defeat on their return to the Championship.
Bowyer said: "I'm delighted with the three points. From start to finish, I thought we were very good and looked solid, limiting them to more half-chances and we had the better clear-cut chances.
"We had a goal disallowed – I'm not sure why – and I thought we deserved to win.
"We always knew a top side like Sheffield United would dominate possession, but we had to limit how often they got around our goal, so I'm very pleased."
Explaining why Manchester United loanee Tahith Chong had to go off, Bowyer said: "His hamstring got a little bit tight.
"Obviously, physically, he joined us late and didn't have as long a pre-season as our boys have had so he's probably not used to playing against a side like Sheffield United who dictate possession the way they did.
"He worked really hard and got a little bit tired towards the end. Hopefully it was just a bit of a tight hamstring and nothing more."
United boss Slavisa Jokanovic said: "We didn't perform badly. They scored with their first shot. This is my general feeling about the game.
"I am of course disappointed with the result. We cannot be happy because we didn't make our supporters happy.
"We showed a lot of things we tried working with. The players showed personality and character, looking to score goals.
"Yes, we need time. I am not unhappy with our effort today. We need to improve some parts of the game but what is really important for us is to improve and be more clinical.
"We need to find a way to be more calm. We will find this way in the future to be successful.
"We are making plans to bring in people but right now I am only thinking about my players here. Tomorrow we can talk about new players. I hope we can bring in players soon."