Ferrer used his speed and ground game to overcome Janowicz's powerful serve with key breaks to finish the first set and start the third.
Ferrer and Almagro have won a combined five titles at this tournament. Along with last year, Ferrer won the event in 2010 and beat Almagro in the 2008 final, ending the latter's two-year title run.
Tursunov ousted Jeremy Chardy of France 6-3, 6-3.
Janowicz had 10 aces with speeds reaching 148 mph on the indoor hard court. but his serve also betrayed him. But four double-faults helped cost him two service games and on match point he twice served into the net.
The third-ranked Ferrer kept scrambling to keep the ball in play until he wore Janowicz down, with one long rally sending Janowicz crashing into a flower stand.
Ferrer also defeated Janowicz in their only previous meeting in the final of the Paris Masters last year when he claimed his first Masters title.
"I knew that today was going to be a different match," Ferrer said. "It was a tough one. He served very well and it was difficult to counter that. It was too bad to drop the second set, but I quickly forgot about it."
Fognini had a strong start at 3-0 and a chance to serve out the first set before Almagro saved a set point in the tiebreaker en route to winning it.
Almagro converted four of five break points to put away the match.