Boss Dean Smith felt the 'fatigue factor' caught up with Walsall after a last-minute goal denied them a win at Chesterfield on Saturday.
Alex Nicholls gave Walsall a 29th-minute lead which they held until the 90th minute, when Jack Lester pounced on a deflected shot to score his first Spireites goal since he returned from three months out with a broken arm.
Chesterfield's second-half pressure merited the 1-1 draw in League One, but Smith felt the midweek FA Cup replay against Dagenham, which went to extra-time and penalties, took its toll at the B2net Stadium.
"We gave them a lot more possession of the ball in the second half but the cruel bit was that the goal came so late after all that effort," Smith said.
"But we probably expected some tired legs after 120 minutes on a really heavy pitch on Tuesday night but we hoped we could have held out and got a deserved three points."