The on-loan Everton striker struck midway through the second half after fellow Merseysider Michael Higdon had put Crewe in front within 38 seconds of the restart.
It was a complete transformation in the Railwaymen's fortunes as they had been out played by the Sky Blues in the first 45 minutes.
With difficult fixtures against Reading, Sunderland and Norwich left in their schedule Dario Gradi's men knew this contest provided their best chance for securing a win to take them over the 50-point mark.
City were well on top early on although they failed to carve clear-cut openings.
Jamaican striker Onandi Lowe unsettled the home defence with his height and strength while Julian Joachim did the same with his pace.
Lowe planted a couple of powerful headers wide of target and Joachim should have scored in the 22nd minute when Gary McSheffrey's corner was scrambled through to him at the far post, but he stabbed his effort wide.
Little was seen of the hosts as an attacking force, until the 40th minute when Steve Jones cut in from the right but dragged his shot wide when well placed inside the box.
Crewe needed a break and were handed it straight at the start of the second period when Jones laid the ball off to Higdon who had been allowed to ghost into a gap in the City backline. And the 21-year-old coolly slotted a right foot shot past the keeper into the bottom corner.
It proved inspirational for the Cheshire side when Kenny Lunt released Symes, and the youngster converted a one-on-one with keeper Scott Shearer.
Lunt's free-kick whistled just past the post but Coventry were back in the game with eight minutes to spare when Lowe was presented with a free header from sub Bjarni Gudjonsson's free-kick.
But Steve Jones helped to wrap things up when he ran half the length of the pitch, outpacing Calum Davenport before he was brought down by Shearer in an attempt to take the ball around the keeper.
Dean Ashton converted the penalty into Shearer's bottom right hand corner to seal the home victory.
Crewe: Williams, Wright, Moses, Foster, Billy Jones, Lunt, Brammer, Cochrane, Steve Jones, Higdon, Symes. Subs: Bankole, Sorvel, Ashton, Varney, McCready.
Coventry: Shearer, Whing, Davenport, Staunton, Warnock, McSheffrey, Deloumeaux, Kerr, Doyle, Joachim, Lowe. Subs: Ward, Shaw, Olszar, Gudjonsson, Barrett.
Referee: F Stretton (Nottinghamshire).