How Suzaku Defeated Bismark

Suzaku won because of limitations of Bismark's Geass.

Suzaku made a suicide move against Bismark. A move that will clearly get him killed. Bismark's geass could predict that and Bismark was prepared to kill Suzaku. However once it became obvious that Suzaku is going to die if that continues, the geass Lelouch cast on Suzaku on Kaminejima island ('to live') saved him again and made him suddenly alter his actions. These altered actions Bismark's geass could not predict so Suzaku not only survived but also managed to defeat Bismark.

I think Bismarks geass can only predict people's intentions rather than everything that will happen. Similar to how Mao reads minds. Because Suzaku's intentions were to die, that all Bismark could get in that situation. That was not enough because of that geass command, Lelouch gave to Suzaku on Kaminejima. That saved Suzaku's life many other times.

I would say Bismark's geass works by reading people's intentions. That is he knows in advance what people plan to do and can use counter measures to stop it. However this ability can be mislead if something else will interfere with intentions of people Bismark fighting. In this case Lelouch's geass command 'to live' from Kaminejima island, interfered with Suzaku's actions. Since it was not in Suzaku's intention to suddenly dodge, Bismark could not see this 'future', that gave Suzaku enough of a unforeseen circumstance to kill Bismark.