Sutherland's 10-game unbeaten run came to an end with a 3-0 defeat to Marconi on Saturday night.
Former Shark James Andrew scored twice for the Stallions to put a halt to Sutherland's NPL 1 finals charge.
Rockdale City saw their own finals hopes dealt a significant blow as they lost 3-1 to Sydney FC.
At Seymour Shaw Park, a win for Sutherland would have kept them within one point of fifth-placed Sydney Olympic with four rounds to play.
Andrew scored either side of half-time before Marko Jesic sealed the result just past the hour mark.
Sutherland coach Terry Palapanis said his side simply weren't good enough.
"Errors again cost us so it's back to square one once more. They dominated us tonight and that cannot be denied," he said.
"We were taught a lesson out there but we'll recover and move on to the next match."
Sutherland will look to keep their faint finals hopes alive when they travel to Wollongong to take on the table-topping Wolves on Saturday night.
At Lambert Park, Aleksandar Canak's strike in first half stoppage time gave Rockdale the lead at half-time against the young Sky Blues.
But a Marco Tilio double seven minutes after the re-start and a late goal to Benjamin Koop gave Sydney FC their first win in five weeks.
"I thought we battled hard in the first half," Rockdale interim coach Nick Porreca said.
"The boys are battling hard with some injuries but a few defensive breakdowns cost us."
The Suns are now in eighth place, three points outside the top five with four games to play.
Rockdale host high-flying Blacktown City at the Ilinden Sports Centre on Sunday.
