Boss Sadler (above) said: “From now on it has to be everyone pulling together.
“It was never going to be easy but we are still that same team (as we were earlier in the season).
“So this is that moment in the sand. We need to move forward and grind things out and be hard-working together.”
The Saddlers had been 12 points clear at one stage on the back of nine straight wins.
Ellis Harrison gave Walsall an early lead, but Jayden Luker struck twice either side of Danny Rose's penalty just before the break as the Mariners completed the turnaround.
Only goal difference separates Grimsby from the play-off places and Luker said: “We mean business. We just have to watch out, stay in our own lane and keep fighting.”
BRADFORD later blew their chance to go top after losing 1-0 at GILLINGHAM, where Conor Masterson scored his first goal for almost a year early in the second half.
“We just didn't have the cutting edge,” said Bantams boss Graham Alexander (inset). "The players kept going, but we just dropped the wrong side of the line.”
SWINDON completed their own remarkable comeback to draw 2-2 at DONCASTER after falling behind to Rob Street's goal inside the opening 20 seconds.
Joe Sbarra doubled Rovers’ lead before the break but Town hit back when substitutes Danny Butterworth and Joe Westley struck in the space of a minute soon after the restart...