Villa - whose introduction sparked applause from both sets of supporters in the 25,525 strong crowd - showed some nice touches, but was otherwise well contained.
It was his first game since scoring for Spain against Australia in the World Cup three-and-a-half months ago.
Sydney almost stole the game in the 86th minute when Terry Antonis rocked the crossbar with a spectacular 30 metre drive and substitute Max Burgess fired wide after pouncing on the loose ball.
A Sydney winner would have been harsh on City, who bossed the game in the first half and had a good share of play in the second.
City, who were missing marquee international Robert Koren through injury, but started the game with four new signings, should have been ahead by the break.
They created most of the noteworthy chances, while hustling Sydney's defence into errors, as the visitors pushed high up the field.
Lively James Brown, who made way for Villa just after halftime, crashed a shot against the crossbar inside the first five minutes.
Janjetovic saved a free kick from Aaron Mooy and Sydney were fortunate to remain on level terms after an awful error from Sasa Ognenovski.
The former Socceroo defender took a horrid air swing at the ball which allowed Mate Dugandzic a clear run at goal, only for the City forward to spray his shot wide.
Dugandzic had another attempt pushed away by Janjetovic, while Sydney struggled to create meaningful chances.
Gameiro had an early shot saved by Andrew Redmayne and Nick Carle wastefully blazed over the bar following a good run and cut back from Sydney captain Alex Brosque.
-AAP