Having been bottom of the table heading into December, the Tykes have rocketed up the standings, having won 12 of their last 15 matches to reach sixth place.
Winger Isgrove started for the side once again, being substituted in the 81st minute, by which point the game was well and truly settled.
Barnsley led after 17 minutes when Ashley Fletcher twisted and turned past two Walsall defenders, before planting a shot in the far corner.
Walsall did level nine minutes later, through Tom Bradshaw’s angled finish, but a quick-fire pair of goals after the break from the visitors put them in total control, as Josh Brownhill lashed home from long range before Harrison Chapman broke forward from halfway and finished smartly at the near post.
Isgrove then had a penalty appeal turned down, after he was brought down at the end of a surging run into the area, but by that stage it didn’t matter.
Gastón Ramírez was also a winner, as he scored both goals in Middlesbrough’s 2-1 home victory over Wolves, as they moved back into the top two of the Championship.
Ramírez headed in at the back post from Adam Clayton’s cross in the 24th minute, before doubling the lead in the 56th minute with a curling, right-footed shot from inside the area that found the far corner.
A Ben Gibson own goal in the 89th minute handed Wolves a consolation, with the result moving Boro to the head of the table, before they dropped to second after Burnley’s win over Blackburn.
There was disappointment for centre-back Jack Stephens, who played the full game for Coventry City, as they lost for a third successive time in League 1, being beaten 1-0 at home by Rochdale.
It had looked like Stephens had saved the Sky Blues a point when he cleared one off the line in the 70th minute.
But Rochdale snatched it in the 89th minute, as Ian Henderson converted from the penalty spot after John Fleck had tripped him in the area.
The result sees Coventry drop to seventh in the table, falling out of the play-off positions.
Striker Sam McQueen came on midway through the second half for Southend United, as they lost 1-0 at home to Chesterfield.
Lee Novak was played through in the 89th minute to slot home the winner, as the Shrimpers failed to register a win for the third successive League 1 match. They have now slipped to tenth, four points off the play-off spots.
Centre-half Jordan Turnbull was due to be in action for Swindon Town at the weekend, but their League 1 fixture away to Oldham was called off due to a frozen pitch.
In League 2, Jason McCarthy played the full game for Wycombe Wanderers, as they missed an opportunity to climb into the play-off spots, losing 1-0 at Newport County.
Scott Boden stroked home John Ayina’s low cross in the 25th minute to give the hosts all three points, condemning Wycombe to a second successive loss.