The European champions named a strong eleven which included star striker Lewandowski and Thomas Muller against Mosimane's Ahly who appeared in their third Club World Cup semi-final.
Bayern looked to settle quickly soon from the start with a smart header from Serge Gnabry flying well off target following a well-weighted delivery from out wide.
It wasn't long before the European treble kings hit the front from good combination play in the area finding Lewandowski to complete the move with a stern finish.
The Cairo Red Devils created their first major threat shortly after going behind with a header from Taher Mohamed, but goalkeeper Manuel Neuer saved.
Mosimane made an injury enforced substitution before halftime as Ali Maaloul was unable to carry on playing through a knock and saw Yasser Ibrahim enter from the bench.
Ahly restarted proceedings in the second half more confident, as Bayern gradually pushed for more goals with threatening balls in and around the six-yard area.
Joshua Kimmich sliced open the Egyptians close to 60 minutes with a teasing ball to David Alaba, but Muller's close-range strike was kept out by Al Ahly shot-stopper Mohamed El-Shenawy.
Mosimane's side battled later on as Ayman Ashraf nearly slotted a cross from Benjamin Pavard into his own net before El-Shenawy parried a header from Eric Maxim Choupo-Moting.
The Bavarians continued to possess dominance up front and had a second goal minutes from time through a clinical header from Lewandowski to confirm the victory and spot in the final with Tigres UANL.