Sabers: Anakin was only described to "perhaps" be the strongest Jedi of all time by the narrator, while very knowledgeable and wise sith like trainee apprentices thought Sirak might be the sith'ari. Though Anakin's every strike was said to "age [Dooku] by a decade", Dooku has very few accolades beyond being formerly considered the greatest Jedi produced in the few centuries of its golden age and one of the greatest in its 25,000 year long history. That doesn't compare with Sirak, who was able to beat trainees so much that they didn't dare challenge him in training matches with training sabers. When he fell, Vader needed a few lightsaber slashes to kill Cin Drallig, but Cin Drallig was only considered to be one of the greatest blademasters of all time at the height of the prime of the Jedi, while Sirak was able to master many lightsaber forms well enough to switch between them while sparring with trainees. Sirak knows too much about lightsaber attacks.
Force: Anakin's strength in the Force was only able to turn Dooku into a helpless joke, but Dooku was only considered one of the most powerful Sith Lords of all time; Sirak has beaten many trainees who were said to be more powerful than soldiers. Anakin may have been able to collapse buildings by screaming and to redirect a 100 meter long transport ship while a padawan, but Sirak can use the Force to sense when trainees are about to hit him. Though Anakin as a padawan can time his fall perfectly to land at terminal velocity on a specific moving, durasteel airspeeder out of a sea of traffic without any injury, Sirak can use the Force to make his movements stronger and faster than trainees can handle. Sirak knows how to use the Force too powerfully.
All-out: Anakin will try to fight Sirak in a duel, but Sirak can easily ragdoll him, as Anakin was only able to trap Dooku with a Force wall according to the AotC novelization while a padawan. Sirak will eventually humor him in melee, and though Anakin was able to render all of Dooku's abilities and power utterly worthless according to the RotS novel's narrator, Sirak can do the same thing to many powerful trainees who had spent many months learning how to spar. Anakin will be defeated, as Sirak is too able to defeat his enemies in fights.