"We had a good talk at Tuesday's training and everybody agreed we let ourselves down. Maybe it was the sort of wake-up call we needed, none of us want to go through that again," Keinzley said. "You can take losing when you play well, it's a different story when you are that bad."
Sunday's match will be the third time in as many seasons United and Napier have clashed in a Chatham Cup fixture. Two years ago is a happy memory because it was then United secured their memorable 2-1 final success but, last season, it was Napier who triumphed in one of the earlier rounds.
United can take some confidence from the 3-1 win recorded over Napier in a Central League match this season - also played at Napier - but Keinzley is quick to point out their talented French recruits, Alsseny Cissoko and Charles Francois Mallman, were unknown factors then and Napier management will have noted the influence they had on proceedings.
"Honestly I wouldn't read a lot into that result, we caught them on the hop a bit and that won't happen again. They will be a hell of a lot tougher this time round."
Keinzley anticipates Napier focusing hard on denying room to the likes of Mallman and other United attackers such as George Jermy, Seule Soromon and Aaron Spierling, and says that will put pressure on his team to move the ball around with speed and precision.
"It's going to be pretty much one-touch football for us, players are going to have to think on their feet. Accuracy is going to be everything and so is discipline, you can bet they won't take any prisoners with their tackling. They'll look to get into our heads, the more they can upset our rhythm the better for them. It's not going to be a game for wimps."
A likely starting XI for United is: Matt Borren, Josh Margretts, Adam Cowan, Waisake Sabatu, Carl Shailer, Nathan Cooksley, Alsseny Cissoko, George Jermy, Seule Soromon, Charles-Francois Mallman, Aaron Spierling.