Christian Benteke's goal rescued a point for Crystal Palace at Leicester - but did he foul Yohan Benalouane? Equally, Leicester's effectiveness on the counter and comfort defending from deep would not seem to present the conditions needed to recover, but recover they did.
But Allardyce's men struck back to earn a crucial point through Yohan Cabaye and Christian Benteke to claim what could yet prove a vital point.
Captain Wes Morgan is out for Leicester's trip to Crystal Palace as boss Craig Shakespeare tries to save him for the Champions League.
"It's a big ask for him because it's a hard injury to get over, in terms of the power and spring for a centre-back".
Leicester appeared set to head into the Atletico match on the back of a victory that would have drawn a line under any lingering relegation fears. I've said that I'm not sure how many points we're going to need for survival.
Five successive league victories - a run that was brought to an end at Everton last Sunday - may have eased concerns Leicester might get drawn into the bottom three but Shakespeare's team selection suggested the manager would not allow a meeting with a team sat two points below the current champions to be overshadowed by Tuesday's tie.
The hosts were the better side in the first half but went in behind and were 2-0 down soon after when Jamie Vardy finished a decisive Foxes breakaway by checking back inside the last defender and curling a left-footed shot into the net.
Surprise of the matchThat Palace had it in them to respond from going two goals down. We could have seen it out if we'd stayed in the lead a bit longer, but they asked a lot of questions of us with their aerial threat.
On Sam Allardyce: "Having worked with Sam in a very short space of time his record there is for all to see". But we must keep picking up points until we're safe.
"We practised it here on the pitch yesterday".
It was the first goal Palace have conceded in their last three home games and they quickly hit back.
"It's that simple. They weren't anywhere near where we put them, sadly which is why he ran in with a free header and scored".
The Eagles are seven points clear of the Premier League drop zone with six fixtures remaining.