Sylla's fortuitous goal gave Holloway's side the lead after seven minutes and Angus MacDonald's 65th-minute own-goal doubled their advantage.
Barnsley were given hope when Tom Bradshaw scored following a mistake by Grant Hall with 11 minutes remaining but QPR held out for a third consecutive home win.
They went ahead when Sylla reacted late to Yeni Ngbakoto's right-wing cross and, in attempting to control the ball, inadvertently nudged it beyond keeper Adam Davies and into the net.
James Perch hit the bar and Jake Bidwell cleared off the line before Sylla was also involved in the second goal, which arrived when MacDonald turned the ball into his own net from close range as he tried to prevent the striker connecting with Pawel Wszolek's right-wing cross.
Barnsley, now beaten on 20 of their last 23 visits to QPR, pulled a goal back when Hall made a mess of his attempt to clear MacDonald's long ball, enabling substitute Bradshaw to round keeper Alex Smithies and score into an empty net.
Sylla, whose goal was his eighth of the season in the Championship, was brought into a much-changed starting line-up along with Ngbakoto, Luke Freeman, Wszolek and Ryan Manning.
QPR boss Holloway saw his changes vindicated as all five players played key roles in a deserved win.
After Perch missed a chance to make it 2-0 by blasting over from Manning's cross, Ngbakoto brought a fine save from Davies with a thumping strike following Wszolek's right-wing delivery.
And Perch went close again on 25 minutes when he headed Freeman's cross against the woodwork from close range.
Barnsley will rue their failure to score during a first-half spell in which they created several chances to equalise.
Josh Scowen and Alex Mowatt sent efforts over the bar, Adam Armstrong had a shot saved by Smithies and Marley Watkins missed two good chances before being denied by Bidwell's goal-line clearance.
Watkins was twice set up by Matty James, heading a cross wide of the target and then shooting over after being put through.
When Watkins showed more composure, this time collecting James' pass and turning away from Hall before firing past Smithies, his shot was superbly kept out by Bidwell at the far post.
It was a different story after the interval, with Freeman and Ngbakoto going close as QPR dominated before eventually getting the all-important second goal.
Additional reporting by the Press Association.