Afobe managed his side's only goal of the game in a 3-1 loss on their return to the Championship.
After getting relegated last term, Stoke want to bounce straight back to the Premier League. But the defeat showed them it will not be an easy season in the Championship.
"We're obviously all disappointed," Afobe told the club's official website.
"I have played in this league for numerous seasons, and it's a tough league. And the boys realised that [on Sunday]. It's a wake-up call and we can hopefully put this behind us.
"There were a lot of things that went wrong today, but I know we are going to learn from this and put things right as soon as possible.
"We will work hard on the training pitch this week, and give our fans a good result and performance this Saturday."