The Chargers inflicted the first defeat of the season on Pete Carroll's side as they put in a dominant performance in their 30-21 win at Qualcomm Stadium.
Allen has revealed that the Chargers were not afraid to challenge Sherman, who is widely regarded as one of the best defensive backs in the NFL.
He told reporters: "He's just a normal guy. We can go at him. We took some shots at him. We are not going to shy away from him. He's not really a shutdown corner.
"We definitely wanted to come out and show we could go any way we wanted to and that we were in control of the game."
Allen caught five passes for 55 yards in his side's first win of the campaign.