Birmingham manager Lee Clark claimed his players suffered from "stage fright" following their 2-0 loss to Middlesbrough.
The Blues, who avoided relegation by the skin of their teeth last season, headed into this Sky Bet Championship campaign brimming with confidence after winning all five of their pre-season fixtures.
Yet they failed to register a shot on target at the Riverside as a fancied Middlesbrough team took the points through goals from Daniel Ayala and £2.8million signing Kike.
Clark, whose side featured 14 new faces, refused to blame the lacklustre showing on Birmingham's busy summer, insisting they have had plenty of time to gel.
He said: "I had them in the first day of pre-season so it is not an excuse. One or two looked like they had a little bit of stage fright.
"It is obviously disappointing to start with a defeat. What has been frustrating is we were quite negative.
"We did not look confident and I do not understand it because we have had a great pre-season.
"The stat of no shots on target tells its own story. It's a little reality check but it's not the end of the world. I have total belief in the players and we can bounce back."
Clark also revealed Birmingham are not finished in the transfer market, with a replacement for midfielder Tom Adeyemi - who joined Cardiff two days ago - already lined up.
"Obviously we have had the unforeseen situation of young Tom going to Cardiff," he added. "We are in negotiations with another club and player."
Clark's mood was in stark contrast to that of opposite number Aitor Karanka, who enjoyed a dream start to his first full season at the helm.
Hopes are high on Teesside after Middlesbrough ended last term by winning six of their final eight games, and the opening day did little to dispel confidence.
Karanka said: "It was very good; a very good result and performance. You never know in the first game of the season.
"We started in the same way as we finished last season, with confidence."
Chief among the positives was the performance of new recruit Kike, whose goal capped a fine debut following his summer move from Real Murcia.
And Karanka revealed Boro beat several other clubs to the striker's signature, adding: "He had offers to go to other Spanish teams. It took a lot of hard work to convince him but we got him."
The only negative for Middlesbrough was the early withdrawal of defender Ben Gibson, who suffered a hamstring injury inside 30 seconds.
"I think he is going to be out for two to four weeks," added Karanka. "But I am not concerned because we have players to replace him."