Keane, on loan from Manchester United, coolly slotted home his first goal for Wednesday from the penalty spot in the 75th minute to cancel out Kenwyne Jones’ early first-half header.
It was a frustrating end to Mandaric’s reign at the club as Wednesday squandered a string of chances, while Cardiff’s winless run was extended to five matches after four straight defeats and did little to ease the pressure on under-fire manager Russell Slade.
An emotional Mandaric, who rescued Wednesday from administration when he took control in December 2010, bade farewell to the club’s fans from the pitch prior to kick-off, thanking them for their “special relationship” during his four-year reign.
Mandaric sold 100 per cent of his shares to Dejphon Chansiri last week and told a grateful Hillsborough that the arrival of the Thai businessman, whose family owns the Thai Union Frozen Group, will “accelerate the club towards the Premier League”.
Wednesday responded to Mandaric’s goodbye speech in the opening minute when Chris Maguire’s shot was turned away by Cardiff goalkeeper Simon Moore, but the visitors had every intention of spoiling the party and were first to strike in the seventh minute.
Defender Scott Malone’s deep cross from the left was met by the off-balance Jones, who deftly steered an angled header beyond Wednesday goalkeeper Keiren Westwood and inside the far post.
Cardiff’s new signing Eoin Doyle pulled a right-footed effort wide when well-placed in the box and went closer to doubling the Wesh side’s lead when forcing Westwood into a sprawling save.
But Wednesday enjoyed decent attacking spells themselves with Maguire firing their best chance wide, his low angled shot coming after a mazy run carried him to the edge of the penalty area.
Seconds after the restart, Wednesday midfielder Jose Semedo’s through-ball set Stevie May on goal but with just Moore to beat the Owls striker’s right-footed effort hit the post.
May, whose six goals in 30 appearances since arriving from St Johnstone in the summer helped prompt the signing of Romanian forward Sergiu Bus this week, then saw another goalbound shot blocked by Cardiff defender Bruno Ecuele Manga.
Wednesday midfielder Sam Hutchinson was next to pass up a golden chance, blazing over the crossbar after debutant Marnick Vermijl’s ball into the area had bounced kindly for him eight yards out.
The home side drew level thanks to Keane’s 75th-minute penalty. Substitute Bus, a transfer deadline-day signing from CSKA Sofia, was shoved over in the area by Matthew Connolly and Keane comfortably converted his spot kick.
Wednesday threatened to snatch all three points in a rousing finish. Substitute Lewis McGugan’s thumping drive was turned away by Moore, who then saved Owls defender Tom Lees’ header from point-blank range.