Janneman and Pieter Malan scored 95 and 53 respectively as the Cobras snapped their losing streak, beating the Lions by 76 runs in Potchefstroom.
The brothers shared a 131-run opening stand, setting the Cobras up for a highly competitive total of 284-5. Zubayr Hamza contributed 40 to the total, while former SA U19 star Jono Bird chipped in with an unbeaten half century.
Lions opener Reeza Hendricks was out early in the innings, and the Johannesburg-based’s batters never capitalised after getting themselves in.
The tournament’s star batsman, Dominic Hendricks, got just 20, while Nicky van den Bergh looked dangerous for his 35 before Bird caught his edge to the wicketkeeper.
Bjorn Fortuin and Eldred Hawkin built a solid lower-order partnership but the pressure of the run chase told on both of them, forcing both to hole out in the deep.
Onke Nyako excelled with the ball for the Cape side, taking 4-29 in his 10 overs.
The winner of Saturday’s Pool B match between the Cobras and Warriors will qualify for the semi-final.