Tursunov ousted Jeremy Chardy of France 6-3, 6-3.
Janowicz hit 10 aces with speeds reaching 238 kph (148 mph) on the indoor hard court, but his serve also betrayed him. Two of his four double-faults helped cost him two service games, and on match point he twice served into the net.
Ferrer, ranked No. 3, kept scrambling to keep the ball in play until he wore Janowicz down, with one long rally even 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 bright start up 3-0 and a chance to serve out the first set before Almagro saved a set point in the tiebreaker en route to finally going up 1-0.
Almagro converted four of five break points to put away the Italian.