Karani struck first in the 30th minute before adding the second in the 60th to help the Sugar Millers climb to second on 28 points, two behind champions Gor Mahia.
At Machakos Kenyatta Stadium, Sofapaka and Ulinzi Stars played to a 1-1 stalemate.
After a goalless first-half, Burundian International Abdul Razak Fiston, gave the hosts the lead in the 48th, heading past keeper James Saruni while Stephen Waruru levelled for the military side in the 64th after heading home Job Muhati’s cross.
Elsewhere, Samuel Onyango netted a double, a goal on each half, as Sony Sugar picked a 2-1 win at home against visiting Muhoroni Youth at the Awendo’s Green Stadium.
In the capital city, substitute Johanna Eric scored a late goal to see Mathare United overcome Thika United 2-1 and record their fourth win of the season.
At the Chemelil Sports Complex, the Bankers woes deepened as they slumped to their fifth consecutive loss to remain rooted at the bottom on six points.
The hosts who have lost only a single match, started on a high with Karani, signed on a free transfer from Mathare United taking 30 minutes to have his name on the score sheet after connecting home Gerson Likonoh’s cross to announce his presence in the cane cutters.
After the goal, Chemelil continued with their dominance and four minutes later, Karani had the chance to double the lead when he picked Likono’s cross but keeper Caleb Wafula denied him.
In the 40th, Mike Mururi charges won a corner that was brought in by Samuel Ouma but defender Mark Odhiambo rose high to clear the danger.
In the second-half, Chemelil picked up where they left after they won a corner that was brought in by Ouma but Odhiambo once again headed it back to the field of play.
In the 54th, KCB made their first substitution, bringing in Andrew Murunga for Tirus Omondi and before the former Tusker forward could settle, Karani completed his brace six minutes later after picking Hillary Echesa’s cross to wave his way through the defence and beat Wafula to find the back of the net for Chemelil’s second goal.
Mururi pulled out Echesa for Stephen Wakhanya while the visitors brought in Benjamin Chaka for in effective John Odhiambo.
In the dying minutes the visitors had a chance to pull one back when Paul Kiongera set Chaka but the latter went for power instead of precision as his shot went wide.
Karani could have sealed his hat-trick a minute later but the forward squandered the glorious chance but that did not trouble him since he had already assured Chemelil of maximum points.
The result was a major upset for KCB head coach Rishadi Shedu who is yet to win a single match since he replaced Abdallah Juma.
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