Only one can return to the top flight, and after a 1-1 draw on Thursday, the hosts merely have to finish the tie level in order to reach Serie A, having finished higher in the standings after 38 matches.
After spurning several gilt-edged chances to score at Cagliari's Unipol Domus in midweek, Bari finally snatched a draw from the jaws of defeat when veteran striker Mirko Antenucci stepped off the bench to steer home a stoppage-time penalty and haul them level.
Coach Michele Mignani - who only last year helped the Puglian club return to the second tier, following several years in the wilderness - intervened at a vital moment, as he replaced luckless striker Walid Cheddira just before the spot-kick was taken.
Having already missed an earlier penalty and a subsequent open goal, Cheddira was among those debating who should attempt to beat Cagliari's Boris Radunovic from 12 yards, but Mignani sent on Antenucci to replace the Morocco international, and the game turned on the 38-year-old's first kick. Incidentally, Bari had also needed a last-gasp Antenucci equaliser to salvage a point in the teams' previous meeting, when they played out a 1-1 draw in February.
Aiming to earn successive promotions back into Calcio's top tier, after 11 years spent in the lower leagues, they now simply have to avoid losing this two-legged playoff tie on aggregate to achieve their goal.
The Galletti finished third in the final league table - five points and one place above Cagliari - so would reach the promised land on that basis should it end all-square after 90 minutes at Stadio San Nicola.
Of course, Cagliari will therefore go all-out for the win, which would see the Sardinian side follow automatically-promoted pair Frosinone and Genoa into Italy's top flight.
However, the Isolani have now failed to beat Bari in three attempts this term - following a draw and defeat in the regular season - but must do so on Sunday in order to return to Serie A at the first time of asking.
It could all have been so different when Gianluca Lapadula steered home an angled header on Thursday, and Radunovic then preserved that advantage with a double save from Cheddira's tame penalty-kick and the rebound. Nevertheless, Claudio Ranieri's men know precisely what their task will be when they walk out in front of nearly 60,000 fans in the Puglian capital.
Ranieri was appointed for a second spell in charge of the club in January, and his team went on to post 60 points to finish fifth in the Serie B standings - enough to qualify for the playoffs' preliminary round.
They then booked their spot in the semis via a 2-1 defeat of Venezia - who were relegated alongside Cagliari last year - before beating Parma over two legs for a place in the promotion decider.
After ending the league season with four straight victories, the Rossoblu have since recorded two wins and two draws during the playoffs, so they may feel an aggregate success remains within their grasp despite how events unfolded in midweek.
Bari captain Valerio Di Cesare withdrew during the warm-up before Thursday's first leg, to be replaced by Slovenian centre-back Zan Zuzek, so Michele Mignani will hope his skipper is fit to feature from the start this weekend.
After being dismissed midway through the Galletti's semi-final second leg, Giacomo Ricci served a suspension in midweek and could also return to the hosts' back four.
Meanwhile, Mirko Antenucci may again have to play the 'supersub' role on Sunday, with Walid Cheddira and Inter loanee Sebastiano Esposito most likely being paired up front.
Fitness permitting, there is no doubt who will lead Cagliari's attack at Stadio San Nicola, as Gianluca Lapadula - who overcame an ankle problem to start and then score the opener in Sardinia - has now netted 26 goals in all competitions this term, including four in the playoffs.
Having set up the Peru striker's goal, Marco Mancosu went off injured later in Thursday's game; should he fail to recover, either Christos Kourfalidis or Nicolas Viola could be drafted in to support Lapadula up front.
Bari possible starting lineup:
Caprile; Dorval, Di Cesare, Vicari, Ricci; Benedetti, Maita, Maiello, Morachioli; Esposito, Cheddira
Cagliari possible starting lineup:
Radunovic; Zappa, Dossena, Goldaniga, Azzi; Makoumbou, Deiola; Nandez, Viola, Luvumbo; Lapadula
We say: Bari 2-1 Cagliari (Bari win 3-2 on aggregate)
As victory is the only option for Cagliari, the onus is on Claudio Ranieri's side to score at least once in Sunday's second leg.
Though Bari failed to fully punish them in midweek, the Isolani were often caught out at the back, and if the home side can take the lead in front of almost 60,000 fans, that could be enough to make a miraculous return to Serie A.
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