Socceroos World Cup aspirant Stamatelopoulos, on loan from Scottish club Motherwell, and Turkish midfielder Ahmet Arslan made their debuts in Saturday night's 2-1 loss to Adelaide United.
The Sky Blues have lost two games on the bounce and three of their past four to slip to fourth on the congested table ahead of Tuesday's clash with second-placed Auckland.
Mere days after signing, Arslan had four shots in the match while 26-year-old striker Stamatelopoulos had three, though neither troubled the scorers.
"They trained with us on Friday, tried to get a lot of information across to both players," coach Ufuk Talay said.
"I thought they both did well when they came on. They both brought us energy, had some moments in the game maybe to capitalise and that's what we wanted from them.
"AP (Stamatelopoulos) hasn't played a lot of games this season so to get 30 minutes was positive.
"Ahmet has played a few more games but not recently, so to get minutes in his legs is also positive too and hopefully we'll continue to build him up."
The coach was confident the January reinforcements would immediately improve Sydney's quality and depth.
"If you look at our bench against Victory (in a 4-0 loss on January 26), it was very young," Talay said.
"Now we've brought in some players with a bit more experience in the game and the reality is it's easier to make changes to influence the game.
"Do these boys come here to sit on the bench? No, they come here to play and be part of the starting XI.
"So the main thing is that we need to get them to that point where they can play 90 minutes."
Talay also played down any concerns over young gun Tiago Quintal, who came off in the 80th minute after going down holding his hamstring.
"Tiago's alright. He was a cramp more than anything else. It wasn't a hamstring so that's very important," Talay said.
"I thought he had a good game and brought us energy. I thought he was trying to make things happen."
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