Hilal were leading 3-0 in steamy Omdurman and ahead on the away-goal rule after a 4-1 first-leg loss when Rostan struck on 92 minutes to book his team a date with FUS Rabat of Morocco or Union Douala of Cameroon.
The vastly experienced Sudanese had patiently chipped away at the three-goal advantage held by African lightweights Sewe with Mohamed al-Tahir scoring in the first half and Mohamed Bisha and Mohamed Traore after the break.
Defeat was a massive blow for Hilal, a club used to progressing much further in African competitions, who have been Champions League semi-finalists three times in the past six seasons. Sewe, who comfortably disposed of Guineans Horoya in the preliminary round last month while Hilal received a bye, were eliminated in the first round during a previous appearance six years ago.
Entente Setif of Algeria also advanced to the final qualifying round thanks to a 4-2 victory over Burkina Faso visitors ASFA Yennenga, who took a 2-1 lead into the return encounter. The 1988 African champions raced into a four-goal lead by the hour mark thanks to a brace from Laid Madouni and one each from Mohamed Amine Aoudia and Khaled Gourmi.
A late Yennenga rally brought goals from Yacouba Ouedraogo and Simplice Yameogo, but a third goal, which would have given the Ouagadougou club a stunning success, eluded them. Kano Pillars of Nigeria are likely to face Setif for a place in the lucrative group phase of the premier African club competition having built a 4-1 first-leg advantage at home three weeks ago against AC Leopards of Congo Brazzaville.