Bartlett had predicted Stilton would be no match for the strengthened title favourites after a poor pre-season, but instead they won 3-2.
Kyial West scored twice for the hosts with Jordan Fiddes also on target. Ian Bradbury and Ash Coddington replied for Harrox.
Bartlett said: “It was a tremendous effort by everyone as we were down to a bare 12 fit players. I was happy to be proved wrong by them!”
Perennial title challengers Netherton United also slipped up on opening day. They went down 2-1 at Long Sutton Athletic after travelling without numerous first-choice players because of holidays, injuries and self-isolation issues.
“We still played okay,” Netherton manager Jon Harrison said. “Two mistakes cost us.”
One bright spot for the city side was a goal for returning star Dan Fountain, although it came after Long Sutton goals from Ryan Alexander and Cameron Lee. Fountain started the season with Peterborough North End.
There was a good start to life in the Premier Division for newly-promoted sides Oundle Town, Stamford Bels and Wittering Premiair.
Nathan Rudman cracked a hat-trick in Oundle’s 5-0 win at Leverington, while Scott Lock, Louie Roberts, Kyle Scott and Josh Dowell netted in Bels’ 4-1 triumph at Crowland.
Will Harris scored both goals as Wittering Pemiair beat Holbeach United Reserves 2-0.