Williamsport (7-10, 5-7) tied it at 5 with four runs in the third, but the Blazers came back against Wildcats reliever Tyler Byers for four in the fourth.
Jason Hammond cracked a three-run homer for Williamsport in the third to tie the game, but it was what the Wildcats failed to do in the fourth inning that became a critical juncture.
Logan Jamison led off with a triple after Cody Englehart couldn't come up with the ball on a diving effort in right field. Connor Arnone drew a one-out walk and stole second.
However, Lesher bore down and got Blake Bandeff on a sharp grounder to Joel Rowe at first and Zach Lucas on a bouncer back to the mound.
"We dug a big hole early and that's what we've been doing, but my team came back," said Williamsport coach Larnie Vickers.
Clear Spring broke the tie in the fourth on a bases-loaded wild pitch that scored Matt Braithwaite, who led with a double. After a sacrifice fly by Lesher, Tyler Walling delivered a run-scoring single and Englehart drove in a run with a double.
With Blazers pitching at a premium after Thursday's debacle, Lesher made it into the seventh, when he was hit hard out of the box as Blake Bandeff doubled and Zach Lucas homered to cut the deficit to 9-7.
Shives called on freshman lefty Walling, who struck out Hammond before yielding a double to Zach Sauble and a deep infield hit to Jake Mann. Walling then retired the next two Wildcats to preserve the win.
"Three games in three days and Brian gave us a much-needed game," said Shives. "He pitched out of jams and ate up the innings.
"After Thursday, this is really a big win for us."
Williamsport outhit Clear Spring 13-8, but Wildcats pitchers yielded nine walks -- five by Mann in the first inning before he was pulled -- and hit three batters.
Lucas had three hits and three RBIs for Williamsport. Hammond had four RBIs.
Glazer and Rowe had two hits each for the Blazers. Glazer is 8 for 10 in his last three games.
"I'm seeing the ball better staying back deep in the zone," said Glazer. "Gotta get hot ... the playoffs are coming up."
Williamsport 104 000 2 -- 7 13 2
Clear Spring 410 400 x -- 9 8 1
Mann, Byers (1), Carr (5) and Butts. Lesher, Walling (7) and Morgan. WP--Lesher (4-2). LP--Byers (0-2). SV--Walling. HR--W: Hammond (3rd, two on), Lucas (7th, one on); CS: Glazer (1st, two on).