Leon Clarke had given the hosts a 28th-minute lead at Bramall Lane only for the Blades to squander numerous chances to put the game beyond Cardiff’s reach.
And they were made to pay in added-on time when Pilkington, on the field for just 12 minutes, volleyed in from close range to the delight of the Welsh club’s travelling fans.
The draw left second-placed Cardiff eight points clear of Fulham, with only the top two teams in the Championship at the end of the regular season assured of promotion to the Premier League.
This result would have been particularly sweet for Cardiff manager Neil Warnock, a boyhood Blades fan and a former Sheffield United boss.
If Cardiff go up, Warnock will have set a new outright English record of eight promotions as a manager.
Next up for Cardiff, unbeaten in 13 games, is a match against table-toppers Wolves, who are currently five points in front of Warnock’s men, although they will kick off eight ahead if they beat Hull on Tuesday.
“That’s what it’s all about, hanging in there,” Warnock told Sky Sports. “When you equalise late on in a game like that, it’s a fantastic feeling.
“It sets us up great for the small matter of Wolves on Friday. We look forward to that.”
Earlier, Britt Assombalonga’s first goal in 14 matches saw Middlesbrough to a 1-1 draw with basement club Burton Albion.
Marvin Sordell’s goal, his first in 19 games, looked as if had secured victory for Burton before Assombalonga equalised in the last minute of the match.
The point saw Middlesbrough stay sixth in the Championship table — the final play-off position.
Teams who finish the regular season, third, fourth, fifth and sixth will then be involved in play-off games, culminating in a Wembley final, to determine which one gets the third and last promotion place.
Brentford remained in the play-off hunt with a 1-0 victory at Bristol City secured by substitute Neal Maupay’s goal 10 minutes from time.
Wales international Tom Lawrence’s free-kick ended Derby’s eight-match winless run with a 1-0 victory over fellow play-off chasers Preston.
“This was a massive result for us,” said Derby manager Gary Rowett. “We needed this win.”
Preston had missed a glorious chance to take the lead in the first half when Alan Browne’s penalty hit the post.
Millwall kept their play-off push going with a 2-2 draw at Ipswich but manager Neil Harris was frustrated despite the south London club extending their unbeaten league run to 14 games.
Jake Cooper gave Millwall a first-half lead only for two goals in as many minutes from Martyn Waghorn to turn the tide in Ipswich’s favour.
George Saville, however, drew Millwall level on the hour mark at Portman Road.
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