Craig Goodwin converted a 76th-minute penalty as in-form Adelaide continued its hot streak, though it needed goalkeeper Joe Gauci to make a crucial late save to deny Patrick Wood an equaliser in stoppage time.
Sydney had 14 attempts but managed just four on target, meaning they slipped to a first defeat against their opponents in 13 league meetings.
Adelaide now sits a point behind leader Central Coast Mariners with a game in hand and is on its longest unbeaten streak since a seven-game run between November 2005 and January 2006.
Just the one goal was enough for Macarthur, too, Denis Genreau on target in a 1-0 triumph over Wellington Phoenix in the early kick-off.
Wellington had lost only one of their previous five games going into the contest, but Genreau was in the right place to tap in a loose ball from close range.
It was the second A-League encounter between the teams, with January's meeting having ended in a 1-1 draw.