Rooney sends City tumbling

Injury-time goal takes United through 4-3 on aggregate, but club face inquiry into missiles thrown at Craig Bellamy

Wayne Rooney last night delivered the ultimate riposte to Manchester City's wealth and ambition, declaring that Manchester United's neighbours "didn't know what to do" in the second half of another extraordinary fixture between the clubs which sent Sir Alex Ferguson into a record seventh League Cup final after a 3-1 win.

In a denouement which mirrored the 4-3 victory over City in September's Premier League game at Old Trafford, Rooney leapt to head home Ryan Giggs' cross in the third minute of second-half injury time, his 21st goal of a productive season sealing victory to set up a Wembley final with Aston Villa on 28 February. "When we were at them they didn't know what to do. They could not get out," Rooney said.

City, who will this morning pursue the £5m signature of Middlesbrough's England Under-21 winger Adam Johnson, have demonstrated across two legs the threat they pose to United's ascendancy, but Ferguson masterminded the win as his side flooded forward after the break.

"I thought Wayne was much better today than he was on Saturday and he scored four goals against Hull," the United manager said. "His control, his leading of the line and his penetration was absolutely fantastic tonight. It was a wonderful performance and a true world-class display."

City's manager, Roberto Mancini, rued the space Rooney was allowed to score. "He's a fantastic player, top player. The next time we must have more attention. If you give one chance to Rooney to score, he will take it."

An investigation will be launched into a missile-throwing attack in which City's Craig Bellamy was hit by a coin in the second half and had a bottle hurled at him by fans. United said last night that two suspects have been identified and arrested. "I didn't see it," Mancini said.

Rooney's goal was bitter luck for City, who seemed to be heading into extra time after Carlos Tevez's superb 76th-minute goal had set the aggregate scores level at 3-3, though their goalkeeper Shay Given had been called upon to make a point-blank save from Darren Fletcher seconds before Rooney pounced. Paul Scholes, integral to United's commanding second-half midfield display, had earlier sent United into a 52nd-minute lead which Michael Carrick extended 19 minutes later.

The police's pleas for players to desist from inflammatory behaviour were also forgotten on an incendiary night in which Luis Nani, Carlos Tevez and Paul Scholes were all booked

City are convinced their bid for Johnson can see off Chelsea's interest. The London club are also understood to be prepared to pay £5m and allow the 22-year-old to stay at the Riverside until the summer to help out Gordon Strachan's side in the Championship. But City's package may be enough to bring in a player who is out of contract the summer.

Robinho was left out of the City squad last night because of the negotiations which seem destined to take him to Santos.

Rio Ferdinand gambled on having a probable three-game ban for violent conduct extended to four, by denying the charge and so enabling himself to play against City, ahead of a Football Association regulatory commission which will sit today to consider his apparent lash at the face of Hull City's Craig Fagan on Saturday.

United's adviser, the former FA compliance officer Graham Bean told Ferdinand that the evidence against him was compelling but he still decided to appeal.