Cardiff were unable to hold onto the lead given to them by Marlon Pack as Toby Sibbick's equaliser earned Barnsley a deserved point from a 1-1 draw in the Sky Bet Championship opener in the Welsh capital.
Pack's header from a corner broke the deadlock in the 54th minute after both teams had earlier efforts ruled out for offside.
But Barnsley - losing play-off semi-finalists last season - showed their resilience to draw level through Sibbick and earn new manager Markus Schopp a draw in his first league match in charge.
The return of Cardiff fans after 18 months away was given more poignancy just before kick-off by a big screen montage of those supporters who had passed away since they last gathered.
The footage closed with a goal scored by - and an image of - Peter Whittingham, the club's gifted former midfielder who died in March of last year from head injuries suffered in a fall at the age of just 35.
There were more tributes to former number seven Whittingham in the seventh minute when a large banner was passed over the heads of Bluebirds fans.
But that gesture coincided with Barnsley almost taking the lead through Carlton Morris.
The midfielder turned Aden Flint in the penalty area but his attempt to curl the ball into the far corner ended with the shot sailing over.
Despite the sense of expectancy in the home crowd, Cardiff were mostly restricted to counter-attacks in the early stages.
Their most direct move should have ended with them going in front, but Ryan Giles' cross into the path of Leandro Bacuna was side-footed over the bar from eight yards.
Giles, a summer loan signing from Wolves, continued to look like Cardiff's biggest threat and his partnership with striker James Collins - another pre-season arrival, from Luton - must have encouraged manager Mick McCarthy.
The Cardiff boss had left Wales striker Kieffer Moore among the substitutes along with Euro 2020 team-mate Ruben Colwill after both players tested positive for Covid-19 last month.
Giles thought he had sparked the opening goal in the 26th minute when his free-kick was headed across goal by Curtis Nelson, and then in by Collins, only to be ruled out for offside.
Barnsley's best effort of the half followed just a minute later when Cauley Woodrow beat Joel Bagan in the box only to see his low shot palmed away superbly by Dillon Phillips.
The visitors' Michal Helik then denied Bagan a goal at the other end with a last-ditch tackle and it remained goalless at half-time.
Another cross by Giles was spooned over by Bacuna, before it was Barnsley's turn to have a goal ruled out for offside.
This time the flag was raised after Dominik Frieser had slotted home from Morris' pass.
But it was Cardiff who took the lead in the 54th minute when an outswinging corner from Giles was met with a firm header from Pack.
It was the midfielder's second successive goal in as many league matches as it was his goal that sent Rotherham down on the final day of last season.
But Cardiff were unable to build on their lead and 15 minutes later, Barnsley equalised through Sibbick.
A superb long pass from substitute Josh Benson released Sibbick, who took the ball in his stride before firing past Phillips in the Cardiff goal.
What the managers said...
Cardiff's Mick McCarthy: "It was emotional and having fans back in was great, it was a shame we couldn't turn it into a win. You won't have a tougher physical game than that and if you aren't going to win, don't get beaten. I've been around a lot of crowds and that was as good as any. I hope we can improve on that and give them something to really shout about. There are about eight things we are unhappy about with their goal, little mistakes.
"We should have kept the press on and then they wouldn't have been able to find that pass. We had the better chances and we both had a goal disallowed. We had two headers straight at the keeper and Leo (Bacuna) had two chances. I think we had the best of it, so there is disappointment. But there is a lot to be happy with. You can't knock the team for effort and work rate and playing for the shirt."
Barnsley's Markus Schlopp: "Having the crowd back again makes the game different. From Barnsley to Cardiff is far so we appreciate all the fans who came. It is nice that we could get a point for them.
"I remember the shot of Cauley (Woodrow) and the finishes of Carlton (Morris). Cardiff also had chances but, over the 90 minutes, we had a bit more."