The Sky Blues delivered their best performance of the season in an exciting clash which was twice delayed due to thunderstorms and a power outage.
Goals to Sofia Huerta, Danielle Colaprico, Savannah McCaskill and a brace to substitute Princess Ibini helped the home side to all three points against a resilient United outfit.
An end to end opening 20 minutes had fans on the edge of their seats before match officials called a stoppage due to a thunderstorm.
After a 45 minute enforced break, The Lady Reds opened the scoring through American import Veronica Latsko shortly after the restart of play.
Sydney's Huerta struck a late blow against her former side as she levelled the score at 1-1 in the final seconds of the first half.
Another Former Red was on the score sheet early in the second half when Colaprico made it 2-1 for the home team, before Latsko locked the scores up at 2-2 with her second goal of the night.
McCaskill gave Sydney the lead after 68 minutes when she bundled the ball over from close range to make it 3-2.
The game took another dramatic turn in the 74th minute when the Cromer Park floodlights switched off forcing another stoppage in play.
Ibini wrapped up the win for the home side with two brilliantly finished efforts in the later stages of the clash.
The win means Sydney moves into third spot on the W-League ladder on nine points, while Adelaide drops to fourth spot.
Next week the Sky Blues travel to Perth to take on Sam Kerr's Glory side and Adelaide host league leaders Melbourne Victory at home.
