The Czech's explosive first-half goal led to Birmingham moving out of the bottom three for the first time since October 2.
It's been a long, harrowing six months but this win gives Birmingham their first real hope of remaining in the Premiership.
Their belated success over Bolton was their first in seven games and the first time they have kept a clean sheet in six matches.
Bolton were not so happy. Following defeats at the hands of Middlesbrough and Manchester United it now appears that the wheels have come off, despite dominating the final 15 minutes in a nerve-jangling finish.
Last autumn this game was called off minutes before kick-off because of fog. It is a fair description to say that both teams were still in a bit of a mist in the early stages of the revised match.
It was important to both with Birmingham's perilous league position causing a great deal of concern at St. Andrew's, while Bolton are desperately keen to play in Europe again next season.
The result was an encounter which was a real battle and not a match which figured highly on the skill scale until Jarosik opened the scoring.
An exception was Jermaine Pennant who really pulled out all the stops in the early stages with his trickery and determined tackling which gave the home fans some much needed encouragement.
But this tailed off as the game developed into a struggle for supremacy with Birmingham showing a little more urgency than Bolton.
But the struggling Midlands club suffered an early setback when Stephen Clemence had to limp off with a leg injury after only eight minutes to be replaced by Stan Lazaridis.
This situation was compounded when Nicky Butt, who had such as a good game against Chelsea last Saturday, was injured after 27 minutes to force manager Bruce to send on Mikael Forssell.
Bolton kept plugging away with Kevin Davies and Stelios Giannakopoulos both missing reasonable first-half chances.
Ominously for Birmingham they failed miserably to carve out any real goal chances with Emile Heskey, who has scored only one goal in 20 games, abjectly failing to pose a single threat as he was kept in check by Tal Ben Haim.
More in hope than expectation Forssell fired a speculative long-range effort over the bar to spark off a spell of concentrated attacking play from Birmingham.
Bolton appeared to be playing well within themselves and suddenly looked dangerous when Abdoulaye Faye unleashed a powerful drive which was roared over the bar.
It must have inspired Jarosik as the Czech Republic international produced an explosive shot in the 37th minute to give Birmingham the lead.
He shrugged off a half-hearted challenge by Jay-Jay Okocha and scored with a swerving 25-yard drive past a helpless Jussi Jaaskelainen.
Seconds later he just failed to add to his tally with a close-range effort.
The second half was a titanic struggle with Birmingham battling to retain their lead which should have been cancelled out by Giannakopoulos, whose close-range effort went just wide.