Will Grigg gave the Saddlers a 30th-minute lead from the penalty spot after Febian Brandy had been fouled, adding his second of the afternoon after 54 minutes with a fine solo effort.
In between he helped set up Craig Westcarr to score his first for the club.
Dave McAllister, able to play for Shrewsbury after the harsh red card he received against Doncaster on Tuesday was rescinded, headed a consolation goal for Town late on.
Turner insisted: "That was the most inept performance we have put in for a long time... partly due to Walsall being a very bright side. In the first 20 minutes we were very poor but I thought we had weathered the first half, but the penalty gave them a boost.
"What was criminal was conceding the second goal right after half-time, which gave Walsall another big boost and we were under the cosh. We rallied later but we can find at this point little excuse for the level of performance."