Shanade Hopcroft then rattled the woodwork early on in the second-half as she struck an effort from inside the box following some good footwork from Sharpe.
Hopcroft then set Sharpe up as she floated a great pass into the winger’s feet, who charged through the Watford half towards the box, but her effort flew wide of the target.
Lambourne ensured she would keep a clean sheet on her league debut for the Eagles as she got up to push a goalbound shot onto her bar, before Aimee Everett cleared the ball away to safety.
Palace’s day was made even more memorable as Isabella Sibley come off the bench to make her first appearance in 11 months, after battling her way back from a serious knee injury.
The three points see Palace stay fourth in the Women's Championship table, just four points off top spot – with a game in hand on leaders Sunderland – and with back-to-back home matches against Lewes (on 12th November in Sutton) and Southampton (on 19th November at Selhurst Park) to come.
Palace: Lambourne (Negri, 69) (GK), Doran, Everett, Nolan, Cataldo, Arthur (Potter, 66), Hopcroft, Guyatt (Filbey, 80), Sharpe (Sibley, 90+2), Hughes, Dennis (Bailey-Gayle, 66)
Subs not used: Johnson
Watford: Goldsmith (GK), Lafayette, Meiwald (Leon, 61), McLean, Baptiste, Johns (Rossiter, 82), Head (Davison, 61), Bennett, Georgiou (Fleming, 54), Chandler, Haines (Wilson, 54)
Subs not used: Harris (GK), Palisch, Reid, Henson