Sir Alex Ferguson branded Manchester United's 2-2 draw with West Brom "inexplicable."
After surprisingly choosing to leave Wayne Rooney on the bench, Ferguson saw his side make the perfect start through the striker's replacement Javier Hernandez.
Nani doubled that fourth-minute advantage before the break as United looked set to stroll home.
But after losing Ryan Giggs to a hamstring injury, United collapsed in a six-minute spell after the interval, with Patrice Evra scoring an own goal before Edwin van der Sar's calamitous mistake presented Somen Tchoyi with an open goal.
"It is an inexplicable result and obviously frustrating," said Ferguson.
"I suppose there are two ways of looking at it. If we were in the middle of the league we could say we were still undefeated. For us it is not good enough."
United have now drawn five times this season, including three on the trot in the Premier League.
They have also tossed away two-goal advantages on three occasions, which cost them precious points here and against Everton, with Dimitar Berbatov coming to their rescue to snatch victory against Liverpool.
"Sometimes it is better to be one goal in front than two. You keep your focus a bit more," said Ferguson.
"But what can you say about their second goal? Edwin van der Sar has probably been playing for 25 years and he was probably in primary school the last time he made a mistake like that.
"You have to just wipe it off the slate. It is not a defining result in terms of where the league is going to end up but we cannot keep doing that."
Ferguson also confirmed Giggs is set for an extended spell on the sidelines after suffering another setback on his comeback after a fortnight out.
The United boss did not even touch on Wayne Rooney, who was dumped on the bench and remained there until 19 minutes before the end.
After openly challenging Ferguson's claim his star striker had been suffering from an ankle injury, it seemed like a decision purely based on form and his eventual introduction on the left wing will not do much to quell talk of a rift between the pair.
It all rather obscured another excellent result for Roberto Di Matteo's side, who have already won at Arsenal this season and seem certain not to get dragged into a relegation fight.
"It was an afternoon of gifts," he said.
"If Manchester United had got a third the game would probably have been over. But I thought it was a correct result.
"Every game has its own history, so I wasn't thinking about their results, but I just felt if we got one back, it might make them nervous."
Di Matteo neatly sidestepped the Rooney issue, insisting there was no feeling of euphoria when he saw the United team-sheet before kick-off.
"Javier Hernandez scored didn't he?" challenged the Italian.
"Manchester United are a squad full of quality players. You look at their team-sheet and think 'oh-oh, they have a strong side there'."
