Former Wales fly-half Ceri Sweeney came on to guide Cardiff Blues to their first win in seven starts as they saw off ex-boss Dai Young's Wasps.
Dan Fish crossed first for the hosts with Elliot Daly replying amid Tom Bell's three first-half penalties.
Another Bell penalty put Wasps 17-10 ahead at the Arms Park.
But Sweeney took over at fly-half from Gareth Davies in the 55th minute, then created a try for Tom James and scored the winner himself.
Sweeney convered his own try to secure the win.
Cardiff Blues: Dan Fish; Tom Williams, Owen Williams, Gavin Evans, Tom James; Gareth Davies, Lewis Jones; Sam Hobbs, Rhys Williams, Taufa'ao Filise, Lou Reed, James Down, Luke Hamilton, Josh Navidi (capt), Robin Copeland.
Replacements: Dafydd Hewitt for T Williams (70), Ceri Sweeney for G Davies (55), Rob Lewis for Jones (60), Nathan Trevett for Hobbs (65), Marc Breeze for R Williams (65), Macauley Cook for Reed (70).
Not Used: Harford, Young.
London Wasps: Elliot Daly; Christian Wade, Chris Bell, Lee Thomas, Jack Wallace; Tommy Bell, Jonah Holmes; Simon McIntyre, T Rhys Thomas, Phil Swainston, James Cannon, Marco Wentzel, Tinus Du Plessis, Sam Jones, Billy Vunipola.
Replacements: Hugo Southwell for L Thomas (65), Charlie Davies for Holmes (56), Will Taylor for Swainston (72), Matt Everard for Du Plessis (60), Dave Hughes for Southwell (73).
Not Used: Morris, Payne, Varndell.
Ref: Luke Pearce (RFU).