It was an ugly scene, and whether the Manchester City left back was trying to make up for a lack of incident in the Barclays Premiership game, who knows, but the force of his blow sent the Portuguese crashing into the advertising hoardings.

As he lay unconscious on the ground, Mendes suffered a fit before being carried off on a stretcher five minutes later and straight to hospital as paramedics administered oxygen and connected him to a drip.

Had Dermot Gallagher, the referee, got a clear view of the incident, he would probably have sent off Thatcher, but having only booked him, which suggested that he saw an infringement, the Welshman may escape censure from the FA.

“We say we’ve had a clampdown, but what’s a red card if that’s not a red card?” Harry Redknapp, an irate Portsmouth manager, said in the aftermath. “What have you got to do to get a red card, kill someone? You pull someone’s shirt or kick the ball away and get booked and then you go and do that and only get a yellow card. They (the FA) have got to look at it, it’s there for all to see.”

Some might have forgiven Thatcher had he not had any previous. He was sent off for two bookings against Shanghai Shenhua during City’s summer tour to China, but it was an elbow that resulted in one of the Shanghai players suffering a collapsed lung during the same match that lingers in the memory.

And the full back received a two-match ban for elbowing Nicky Summerbee while playing for Wimbledon against Sunderland in January 2000. Worse still, the attack on Mendes was not his first of the game. He also raised arms at Sean Davis, Kanu and Benjani Mwaruwari, which escaped the attention of Gallagher.

“I knew it was coming five seconds before it came,” Redknapp said. “As soon as I saw Ben Thatcher, I knew what was going to happen. I would have bet my life on it being a banger. Off the field, you couldn’t meet a nicer boy. Unfortunately, when he is on the pitch he does things like that.”

Redknapp’s comments were echoed by Matt Taylor. “It was a disgrace,” the Portsmouth midfield player said. “Thatcher needs to have a look at himself.”

Stuart Pearce claimed not to have seen the incident properly. “I hope it (the video evidence) shows it was accidental, but if it does not, I think the disciplinary action will come from elsewhere,” the City manager said.

David James, who was cheered on his return after signing for Portsmouth a fortnight ago, would probably have been hard pressed to remember the previous time an opposition goalkeeper was given such an easy ride at the City of Manchester Stadium. But he still had more to do than Nicky Weaver in the City goal, who, with the exception of a splendid save from Taylor in the 68th minute, was redundant.

Joey Barton and Ishmael Miller had City’s best chances, but the mind had drifted to thoughts for Mendes’s health long before the final whistle.

MANCHESTER CITY (4-4-2): N Weaver — M Richards, R Dunne, S Distin, B Thatcher — T Sinclair, C Reyna (sub: S Ireland, 66min), J Barton, G Samaras (sub: I Miller, 71) — D Vassell, P Dickov. Substitutes not used: J Hart, O Dabo, D Mills. Booked: Sinclair, Thatcher.

PORTSMOUTH (4-4-2): D James — G Johnson, L Primus, S Campbell, D Stefanovic — G O’Neil, S Davis, P Mendes (sub: R Hughes, 52), M Taylor — Kanu, B Mwaruwari (sub: S Todorov, 65). Substitutes not used: N Jordan, D Thompson, N Pamarot. Booked: Davis.

Referee: D Gallagher.