African champions Setif suffer huge blow
Alaeddin Yousef converted a penalty four minutes before half-time but failed from another spot-kick before Ghanaian Augustine Okrah sealed success with a late goal.
Setif, who last year conquered Africa for the second time, suffered a major setback late in the first half of the matchday 4 clash when twice-cautioned Ryad Keniche was red-carded.
USM Alger clinched a semi-final place from Group B Friday with a 1-0 win at fellow Algerians Mouloudia El Eulma via a Mohamed Meftah header.
That result left Merrikh and Setif fighting for second spot and victory in Omdurman moved the Sudanese Red Devils three points above the Algerian Black Eagles.
If Setif lose at USM on August 21, Merrikh will reach the semi-finals of the marquee African club football competition for the first time.
And even if the title-holders triumph and avenge a matchday 1 home defeat by USM, Merrikh can book a knockout place by winning at pointless Eulma the following day.
Four-time African champions TP Mazembe of the Democratic Republic of Congo top Group A with eight ponts after a 1-0 win over bottom club Smouha of Egypt in Lubumbashi.
Moghreb Tetouan of Morocco joined Al Hilal of Sudan on five ponts after a shock 1-0 victory in Omdurman courtesy of an Ahmed Jahouh penalty.
Champions League contenders are chasing a $1.5 million (1.35 million euros) first prize and a place at the 2015 FIFA Club World Cup in Japan.