Ten-man Forest Green held on to edge out Conference newcomers Cambridge.
Gadsby's inch-perfect cross set up Rovers' winner
The U's were on top for large periods of the first half but both Andy Duncan and Fola Onibuje were unable to beat keeper Ryan Clarke from close range.
And Rovers made the visitors pay when Scott Rendell headed home Matt Gadsby's cross four minutes after the restart.
Rovers had Abdou Sall sent off for a professional foul on 63 minutes but the U's failed to capitalise and Onibuje missed another good headed chance.
Forest Green: Clarke, Richardson, Sall, Graham, Gadsby, Meechan, Wanless, Searle, Simpson, Rendell (Haldane 71), Teixeira (Beswetherick 66).
Subs Not Used: Harrison, Garner, Gosling.
Sent Off: Sall (64).
Goals: Rendell 49.
Cambridge:Behcet, Gleeson, Duncan, Peters, Chick (Duffy 60), Angel (Okai 80), Bridges, Quinton (Daniels 89), Smith, Turner, Onibuje.
Subs Not Used: Davies, Nolan.
Referee: P Gibbs (West Midlands).