Alan Pardew's men - who remain two points behind the Blades and in 18th place - had taken the lead through a long-range effort from Talal El Karkouri on the hour.However, they then sat back and invited pressure from the visitors, who levelled through Jon Stead with 20 minutes left.
Neither side could find a winner, and although they each gained ground on fellow strugglers Wigan - who lost at Liverpool - matches are fast running out to save their top-flight status.
The Valley had been baked in sunshine on a fine spring afternoon in south-east London.
The home faithful were rocking after an ABBA tribute band warmed them up for what was certainly a `Winner Takes It All' encounter.
• Pardew takes positives from draw
Charlton legend Derek 'Killer' Hales called on the Red Army to find their voice as he rallied the crowd with a pitch-side walk-on just before kick-off.
With the atmosphere set, the opening exchanges were just as electric.
Winger Dennis Rommedahl was also pushed forwards down the right flank as Charlton started at full throttle.
The game was less than three minutes old before referee Alan Wiley had his yellow card out.
Keith Gillespie sent in a low cross from the right - and Luton Shelton dived through the six-yard box to try and knock the ball in with his hand, leaving the referee little option but to go for his pocket.
Both sides looked dangerous on the counter-attack.
After 13 minutes, Rommedahl - out of contract this summer - skipped away down the right and his low centre flashed across the six-yard box.
The flying Dane was soon clear again, this time chipping the ball up for Darren Ambrose, whose looping header dropped just wide.
England striker Darren Bent shot wide at the near post following a well-worked corner from Ambrose.
After 19 minutes, Blades keeper Paddy Kenny tipped over a curling 25-yard free-kick from El Karkouri.
Kenny was soon scrambling down to his right to push Thomas' 25-yard drive behind.
The Charlton winger then conceded a free-kick in a dangerous position at the other end for a late sliding challenge on Nick Montgomery.
However, from just outside the `D' on the left, Tonge struck his shot straight into the wall.
United were now enjoying a decent spell of pressure. After 35 minutes, Gillespie forced a fine one-handed save from Scott Carson at the far post following Armstrong's deep left-wing cross.
As half-time loomed, Charlton looked to play some football in the visitors' half again.
However, once more there was no telling pass to open up the Blades defence.
After a slow start to the second half, slowly Charlton came to life as the hour mark approached.
A chipped pass from Zheng Zhi almost found Jerome Thomas in the right side of the Blades penalty area.
Then out of nothing, Charlton took the lead. There looked to be little danger when Karkouri picked the ball up just inside the visitor's half on 59 minutes.
The Moroccan defender strolled forwards and unleashed a 35-yard low drive, which took a slight deflection off the boot of Tonge and flew past Kenny low into the bottom right corner.
The relief was clear around The Valley - but Sheffield United immediately went on the attack.
Stead flashed a header over the bar from a left-wing free-kick.
Charlton continued to sit back and invite pressure. United, though, failed to make the most of their possession - which included two free-kicks in dangerous positions around the 18-yard box.
However, the Blades were level on 70 minutes. Nick Montgomery fed Stead on the right side of the penalty area.
The former Sunderland and Blackburn striker took a touch before drilling an angled drive into the far corner.
With 15 minutes left, Charlton boss Alan Pardew sent on veteran striker Jimmy-Floyd Hasselbaink in an attempt to win the match, replacing Thomas and going to 4-4-2.
The Blades, though, always looked dangerous on the break. In the end, neither side could find a winner, despite five minutes of stoppage time.
The visitors will have gone away happier with the point, their fans chanting 'we are staying up' at full-time - but the Blades will need a few more yet before they are home and dry.
Pardew takes positives from draw
Alan Pardew admitted Charlton's 'percentage chance' of staying in the
Barclays Premiership dropped following today's 1-1 draw with fellow relegation
battlers Sheffield United at The Valley.
The Addicks remain in 18th place, two points behind the Blades and Wigan.
Although both sides gained ground on the fast-fading Latics, the matches with
which to save their top-flight status are running out as the season heads
towards a thrilling climax.
Charlton had taken the lead through a deflected, long-range effort from Talal
El Karkouri on the hour.
However, rather than controlling the destiny of the match, the home side had a
'wobbly five minutes', sat back and invited pressure.
The Blades eventually drew level when Jonathan Stead drilled in an angled
drive from the edge of the box to ensure a hard-fought share of the spoils.
With a trip to Blackburn next weekend, followed by the visit of Tottenham and
a final-day clash at Liverpool, Pardew maintains there is still 'all to play
for'.
The Charlton boss said: 'In terms of us staying up, the percentage chance
will have gone down after the result.
'But I am still looking at the fixtures which we have - and I am not looking
at anyone else's - because we have three games left and we need to take what we
have done today into the next match.
'There are positives to come out of it, because for 70 minutes it was a
strong, well-disciplined performance.
'Unfortunately the goal seemed to affect us in a negative way.
'I thought we got a little bit rash, a bit over-eager and were so desperate
to win. We just needed to survive a wobbly five minutes, which we did not
managed to do.
'Even the officials got wrapped up in the tension of it all. I was desperate
to get some subs on because Ben Thatcher was struggling with a hip injury - and
that player was then involved in the goal for them.'
Pardew added: 'Sheffield United came here and used all the tricks away from
home to try to slow us down and kill the tempo, but we would not give into that.
We chased the game at the end, but with no joy.
'We have not got the result we wanted today, but the other results have gone
our way. Now with three games to go, it is all to play for and there is maybe
five clubs involved. It is going to be tense.
'We obviously need one more win for sure, and that might be enough. Who
knows?
'We will just go into the match next week at Blackburn trying to win and see
where we are.'
The visiting fans were chanting 'we are staying up' at the final whistle.
However, there is still some work ahead yet before they can pop the champagne
corks in South Yorkshire.
Blades boss Neil Warnock declared: 'If you look at our record against the
bottom six sides, we are miles ahead at the top of the league - now we have to
continue that over the final three games.
'There is pressure on everybody, but maybe not as much on us because everyone
expected Sheffield United to be in there.
'Charlton are not down because they have failed to beat us.
'It is amazing what you can do with a group of players who believe. We knew
we had to stand up and be counted today.
'We have a gritty bunch of players, which showed out there - and I thought
referee Alan Wiley was outstanding, which is unusual for me.
'It was one of the best performances I have seen as a manager, and thank
goodness he was in charge.'
Warnock was full of praise for Stead, who endured a tough time at Sunderland
and arrived at Bramall Lane in a cut-price £750,000 deal in January.
He said: 'I think he has been very harshly treated. When he was at Blackburn
at few years ago, he kept them up single-handedly.
'That probably went a little to his head and he has had a couple of difficult
seasons.
'Maybe too many expectations were on Jon. But since he has come to us he has
been a breath of fresh air.
'His goal today was like an exocet missile.'
Charlton Athletic 1 - 1 Sheffield United
