Birmingham City 1 Manchester United 3: Saha fires United as fans turn on Bruce

His team were well on their way to their seventh home defeat of the season when Steve Bruce made the innocent mistake of acknowledging the only section of supporters in St Andrew's who cared enough to sing his name. The Manchester United fans had chanted insistently for their former captain to wave at them and, when he did so, the Birmingham City manager was greeted with a barrage of boos from his own fans.

Defeated in the Carling Cup quarter-finals and 19th in the Premiership, after almost four years in charge of Birmingham, Bruce has reached a crisis point. The club's chairman, David Gold, said earlier in the day that Birmingham had no intention of sacking their manager before the January transfer window but if that was the official vote of confidence from the board, then the straw poll on the terraces sounded very different.

Booed off at the end of a defeat inflicted by two goals from Louis Saha, and a first for United from Park Ji-Sung, Bruce's team were never really close to troubling United, who conceded a late header from Jiri Jarosik. The Birmingham manager took his time coming up to speak after the match - Sir Alex Ferguson always had words of advice in times of trouble - but when he arrived at last he was bullish about his relationship with the St Andrew's fans.

"I have been here four years as a manager and two years as a player," he said. "I have been here nearly as long as I was at United and the Birmingham fans know what I think about this club. I don't understand [the allegation] that they reacted like that, not that I'm worried about it."

The Carling Cup semi-finals may not be quite what the Glazers had in mind when they defined a successful first half of the season as the new owners of United, but for Sir Alex Ferguson any competition will do at the moment. His mid-week evenings next year have already been freed up by United's failure to get past the group stages of the Champions' League but judging by the team Ferguson selected last night it did not appear he wanted any more spare time.

Gary Neville, Mikaël Silvestre, Cristiano Ronaldo, Darren Fletcher and Wes Brown were part of a strong United side that started the match but it was on the substitutes' bench that Ferguson made his intentions plain. Both Wayne Rooney and Rio Ferdinand were there in case of emergency and it was the introduction of the 20-year-old striker after the interval that panicked Birmingham into conceding their first goal within 30 seconds of the re-start.

"I think the presence of Wayne helped us a bit," Ferguson said, "I was satisfied with the performance and I think they played well. We maybe should have had a couple of goals in the first half but the three quick goals put us in a great position. I am delighted for Park, he has been very close before and it was a great goal for him."

United began as if they might end the contest in the first 10 minutes. Giuseppe Rossi, the Italian-American acquired from Parma last year, struck the bar when John O'Shea headed down Ronaldo's cross from the right. Saha connected with Fletcher's ball to the back post but could not steer it home. On 42 minutes, Emile Heskey fashioned the best chance of the half with a turn and shot that drew an exceptional save from Tim Howard.

It could just have been the sight of Manchester United's lantern-jawed No 8 coming out in the second half, but Birmingham crumbled within minutes without an intervention from Rooney. The first goal came just 30 seconds into the half, an intricately worked move down the right wing that saw Park lay the ball off to Ronaldo who crossed for Saha to score.

The Frenchman was also central to Park's first goal for United, shielding the ball in the area on 49 minutes and allowing the South Korean to take on possession and strike a rising shot inside Maik Taylor's near-post. Gary Neville made the third for Saha from the right, picking out the striker, who struck a vicious rising shot into the net.

"I was very, very pleased with the way we performed in the first half. We played so well that United had to make a change," Bruce said. "They brought on a big name and it was a terrible, terrible start and within four minutes the cup tie was over which was a shame. Then you need people to roll up their sleeves and try to stay in it - which they did."

The only blemish on a strong United performance came when Jarosik headed in Jermaine Pennant's free-kick on 75 minutes. By then Nicky Butt, who put in a performance well below the standards he set at United, had been substituted and resisted the temptation to repeat his manager's wave to the away fans. Birmingham's problems are not hard to see, for United the real test will be cutting Chelsea's lead over Christmas.

Birmingham City (4-4-2): Taylor; Johnson, Taylor, Upson, Painter; Pennant, Butt (Clapham, 67) Clemence, Dunn (Kilkenny, 66); Jarosik, Heskey (Forssell, 82). Substitutes not used: Doyle (gk), Pandiani.

Manchester United (4-4-2): Howard; Neville, Silvestre (Ferdinand, 60), Brown, Richardson; Ronaldo, Fletcher, O'Shea (Jones, 66), Park; Saha, Rossi (Rooney, h-t). Substitutes not used: Van der Sar (gk), Bardsley.

Referee: M Halsey (Lancashire).