The Europa Conference League Champions Roma remained on track for a second European trophy in two seasons, after a 0-0 draw at Bayer Leverkusen sent them through 1-0 on aggregate on Thursday.
Mourinho, known for his defensive tactics, has stayed true to form this Europa League season, with the Europa Conference League holders conceding just three goals in eight knockout games on the way to the final.
Leverkusen, who have beaten Bayern Munich, Atletico Madrid and RB Leipzig at home this season, started brighter, with 20-year-old creator Florian Wirtz pulling the strings in midfield.
With a deficit to overturn, Leverkusen were on the front foot early on and Diaby came close to levelling the tie after being sent clear down the right, only for his fierce effort to rattle the bar and bounce clear.
The visitors held on through eight minutes of added time and will face Sevilla in the final in Budapest in late May.